diff --git a/WHATS_NEW.md b/WHATS_NEW.md
index d82b808b..25fe4b24 100644
--- a/WHATS_NEW.md
+++ b/WHATS_NEW.md
@@ -2,6 +2,12 @@
 
 ## What's new (2026-06-26)
 
+### Theme-Invariant Matching (Light Template, Dark Mode)
+
+Find a button captured in light mode even after the app switches to dark mode. Full reference: [`docs/source/Eng/doc/new_features/v217_features_doc.rst`](docs/source/Eng/doc/new_features/v217_features_doc.rst).
+
+- **`normalize_theme` / `match_theme`** (`AC_match_theme`): `match_template` correlates raw pixel intensities, so a light-mode template scores terribly against the same control in dark mode — the polarity is inverted. The fix is to compare *structure*. `normalize_theme` maps an image to a polarity-invariant single channel (`sobel`/`laplacian` gradient magnitude — identical for an image and its colour inverse — or `zscore`); `match_theme` normalizes both the template and the screen, then locates the template via `visual_match.match_template`, finding it across a light/dark flip that defeats raw matching. cv2/numpy are imported lazily so the module stays importable everywhere. Fourth feature of the ROUND-15 perception lane. No `PySide6`.
+
 ### Sample a Region's Text Contrast (WCAG)
 
 Grade the legibility of on-screen text when you only have a region, not the two colours. Full reference: [`docs/source/Eng/doc/new_features/v216_features_doc.rst`](docs/source/Eng/doc/new_features/v216_features_doc.rst).
diff --git a/docs/source/Eng/doc/new_features/v217_features_doc.rst b/docs/source/Eng/doc/new_features/v217_features_doc.rst
new file mode 100644
index 00000000..dccaecca
--- /dev/null
+++ b/docs/source/Eng/doc/new_features/v217_features_doc.rst
@@ -0,0 +1,49 @@
+Theme-Invariant Matching (Light Template, Dark Mode)
+====================================================
+
+``match_template`` correlates raw pixel intensities, so a template captured in
+light mode scores terribly against the same control in dark mode — the polarity
+is inverted. The fix is to compare *structure* (edges, gradients), which is the
+same regardless of which way the colours run. ``theme_normalize`` turns an image
+into a polarity-invariant representation before matching.
+
+* :func:`normalize_theme` — map an image to a normalised single-channel image.
+  ``sobel`` (default) and ``laplacian`` use gradient magnitude, which is
+  identical for an image and its colour-inverse; ``zscore`` standardises
+  intensity.
+* :func:`match_theme` — :func:`normalize_theme` both the template and the
+  haystack (the screen by default), then locate the template — finding it across
+  a light/dark theme flip that defeats raw matching.
+
+``cv2`` / ``numpy`` are imported lazily, so importing the module never requires
+them, and the locating logic reuses :func:`visual_match.match_template`. Imports
+no ``PySide6``.
+
+Headless API
+------------
+
+.. code-block:: python
+
+    from je_auto_control import match_theme, normalize_theme
+
+    # A button template grabbed in light mode, found in the dark-mode app:
+    hit = match_theme("save_button_light.png", method="sobel", min_score=0.4)
+    if hit and hit["score"] >= 0.5:
+        click(hit["x"] + hit["width"] // 2, hit["y"] + hit["height"] // 2)
+
+    # The transform itself (e.g. to feed your own matcher):
+    edges = normalize_theme("template.png", method="sobel")
+
+Because gradient magnitude is identical for an image and its inverse,
+``normalize_theme(img, "sobel")`` equals ``normalize_theme(255 - img, "sobel")``
+— that invariance is exactly what lets one template match both themes. Use
+``min_score`` lower than for raw matching (structure correlation runs cooler).
+
+Executor commands
+-----------------
+
+``AC_match_theme`` (``template`` + ``region`` ``[x, y, w, h]`` / ``method`` /
+``min_score`` → ``{found, x, y, width, height, score}``) locates a template
+across a theme flip. It is the matching read-only ``ac_match_theme`` MCP tool and
+a Script Builder command under **Image**. :func:`normalize_theme` (which returns
+an image array) is the Python-API surface.
diff --git a/docs/source/Zh/doc/new_features/v217_features_doc.rst b/docs/source/Zh/doc/new_features/v217_features_doc.rst
new file mode 100644
index 00000000..83c82f8c
--- /dev/null
+++ b/docs/source/Zh/doc/new_features/v217_features_doc.rst
@@ -0,0 +1,41 @@
+主題不變比對(淺色模板、深色模式)
+==================================
+
+``match_template`` 以原始像素強度相關比對,故在淺色模式擷取的模板,對深色模式下同一控制項評分極差——
+極性反轉了。修法是比較*結構*(邊緣、梯度),不論顏色走向如何皆相同。``theme_normalize`` 在比對前
+把影像轉成極性不變的表示。
+
+* :func:`normalize_theme` ——把影像映射為正規化的單通道影像。``sobel``(預設)與 ``laplacian``
+  使用梯度幅值,對影像與其顏色反相版本相同;``zscore`` 將強度標準化。
+* :func:`match_theme` ——對模板與 haystack(預設為螢幕)都做 :func:`normalize_theme`,再定位模板——
+  即使在會擊敗原始比對的淺/深主題切換下也能找到。
+
+``cv2`` / ``numpy`` 採延遲匯入,故匯入本模組永遠不需要它們,定位邏輯則重用
+:func:`visual_match.match_template`。不匯入 ``PySide6``。
+
+無頭 API
+--------
+
+.. code-block:: python
+
+    from je_auto_control import match_theme, normalize_theme
+
+    # 淺色模式擷取的按鈕模板,在深色模式的 app 中找到:
+    hit = match_theme("save_button_light.png", method="sobel", min_score=0.4)
+    if hit and hit["score"] >= 0.5:
+        click(hit["x"] + hit["width"] // 2, hit["y"] + hit["height"] // 2)
+
+    # 轉換本身(例如餵給你自己的比對器):
+    edges = normalize_theme("template.png", method="sobel")
+
+由於梯度幅值對影像與其反相版本相同,``normalize_theme(img, "sobel")`` 等於
+``normalize_theme(255 - img, "sobel")``——正是這個不變性讓單一模板能比對兩種主題。
+``min_score`` 請設得比原始比對低(結構相關分數較低)。
+
+執行器指令
+----------
+
+``AC_match_theme``(``template`` 加上 ``region`` ``[x, y, w, h]`` / ``method`` /
+``min_score`` → ``{found, x, y, width, height, score}``)跨主題切換定位模板。以對應的唯讀
+``ac_match_theme`` MCP 工具及 Script Builder 指令(位於 **Image** 分類下)形式提供。
+:func:`normalize_theme`(回傳影像陣列)則是 Python API 介面。
diff --git a/je_auto_control/__init__.py b/je_auto_control/__init__.py
index 4c0193c0..bfb1a716 100644
--- a/je_auto_control/__init__.py
+++ b/je_auto_control/__init__.py
@@ -141,6 +141,8 @@
 from je_auto_control.utils.contrast_map import (
     dominant_pair, grade_contrast, region_contrast,
 )
+# Theme-invariant matching so a light template matches dark mode
+from je_auto_control.utils.theme_normalize import match_theme, normalize_theme
 # Rich clipboard formats — RTF + CSV/TSV codecs and Windows get / set
 from je_auto_control.utils.clipboard_rich_formats import (
     build_rtf, csv_to_rows, get_clipboard_csv, get_clipboard_rtf, rows_to_csv,
@@ -1768,6 +1770,7 @@ def start_autocontrol_gui(*args, **kwargs):
     "simulate_cvd", "colors_collide", "color_distance",
     "place_labels", "label_color",
     "grade_contrast", "dominant_pair", "region_contrast",
+    "normalize_theme", "match_theme",
     "build_rtf", "rtf_to_text", "rows_to_csv", "csv_to_rows",
     "set_clipboard_rtf", "get_clipboard_rtf",
     "set_clipboard_csv", "get_clipboard_csv",
diff --git a/je_auto_control/gui/script_builder/command_schema.py b/je_auto_control/gui/script_builder/command_schema.py
index 42fcfc56..1d1f6f0f 100644
--- a/je_auto_control/gui/script_builder/command_schema.py
+++ b/je_auto_control/gui/script_builder/command_schema.py
@@ -4591,6 +4591,21 @@ def _add_work_queue_specs(specs: List[CommandSpec]) -> None:
         ),
         description="Sample a screen region and grade its text contrast.",
     ))
+    specs.append(CommandSpec(
+        "AC_match_theme", "Image", "Match (Theme-Invariant)",
+        fields=(
+            FieldSpec("template", FieldType.STRING,
+                      placeholder="template image path"),
+            FieldSpec("region", FieldType.STRING, optional=True,
+                      placeholder="[x, y, w, h]"),
+            FieldSpec("method", FieldType.STRING, optional=True,
+                      default="sobel",
+                      placeholder="sobel / laplacian / zscore"),
+            FieldSpec("min_score", FieldType.FLOAT, optional=True,
+                      default=0.5),
+        ),
+        description="Locate a template across a light/dark theme flip.",
+    ))
     specs.append(CommandSpec(
         "AC_normalize_ext", "Shell", "Normalize Extension",
         fields=(
diff --git a/je_auto_control/utils/executor/action_executor.py b/je_auto_control/utils/executor/action_executor.py
index 4456d9ae..6ba236f4 100644
--- a/je_auto_control/utils/executor/action_executor.py
+++ b/je_auto_control/utils/executor/action_executor.py
@@ -2900,6 +2900,18 @@ def _region_contrast(region: Any = None) -> Dict[str, Any]:
     return region_contrast(region=_coerce_region(region))
 
 
+def _match_theme(template: Any, region: Any = None, method: Any = "sobel",
+                 min_score: Any = 0.5) -> Dict[str, Any]:
+    """Adapter: locate a template across a light/dark theme flip (device)."""
+    from je_auto_control.utils.theme_normalize import match_theme
+    match = match_theme(str(template), method=str(method),
+                        min_score=float(min_score),
+                        region=_coerce_region(region))
+    if match is None:
+        return {"found": False}
+    return {"found": True, **match}
+
+
 def _normalize_ext(target: str) -> Dict[str, Any]:
     """Adapter: the lowercased extension of a path / bare ext (pure)."""
     from je_auto_control.utils.file_assoc import normalize_ext
@@ -6938,6 +6950,7 @@ def __init__(self):
             "AC_grade_contrast": _grade_contrast,
             "AC_dominant_pair": _dominant_pair,
             "AC_region_contrast": _region_contrast,
+            "AC_match_theme": _match_theme,
             "AC_normalize_ext": _normalize_ext,
             "AC_file_association": _file_association,
             "AC_get_control_text": _get_control_text,
diff --git a/je_auto_control/utils/mcp_server/tools/_factories.py b/je_auto_control/utils/mcp_server/tools/_factories.py
index ab53fde9..4369522b 100644
--- a/je_auto_control/utils/mcp_server/tools/_factories.py
+++ b/je_auto_control/utils/mcp_server/tools/_factories.py
@@ -4091,6 +4091,22 @@ def img_histogram_tools() -> List[MCPTool]:
             handler=h.region_contrast,
             annotations=READ_ONLY,
         ),
+        MCPTool(
+            name="ac_match_theme",
+            description=("Locate a 'template' image on screen across a "
+                         "light/dark theme flip, by matching gradient "
+                         "structure ('method' sobel/laplacian/zscore). "
+                         "'region' [x,y,w,h] clips the search. Returns {found, "
+                         "x, y, width, height, score}."),
+            input_schema=schema({"template": {"type": "string"},
+                                 "region": {"type": "array",
+                                           "items": {"type": "integer"}},
+                                 "method": {"type": "string"},
+                                 "min_score": {"type": "number"}},
+                                required=["template"]),
+            handler=h.match_theme,
+            annotations=READ_ONLY,
+        ),
     ]
 
 
diff --git a/je_auto_control/utils/mcp_server/tools/_handlers.py b/je_auto_control/utils/mcp_server/tools/_handlers.py
index ed3bd986..5006b182 100644
--- a/je_auto_control/utils/mcp_server/tools/_handlers.py
+++ b/je_auto_control/utils/mcp_server/tools/_handlers.py
@@ -769,6 +769,11 @@ def region_contrast(region=None):
     return _region_contrast(region)
 
 
+def match_theme(template, region=None, method="sobel", min_score=0.5):
+    from je_auto_control.utils.executor.action_executor import _match_theme
+    return _match_theme(template, region, method, min_score)
+
+
 def normalize_ext(target):
     from je_auto_control.utils.executor.action_executor import _normalize_ext
     return _normalize_ext(target)
diff --git a/je_auto_control/utils/theme_normalize/__init__.py b/je_auto_control/utils/theme_normalize/__init__.py
new file mode 100644
index 00000000..1c75d90e
--- /dev/null
+++ b/je_auto_control/utils/theme_normalize/__init__.py
@@ -0,0 +1,6 @@
+"""Theme-invariant image normalisation so light templates match dark mode."""
+from je_auto_control.utils.theme_normalize.theme_normalize import (
+    THEME_METHODS, match_theme, normalize_theme,
+)
+
+__all__ = ["normalize_theme", "match_theme", "THEME_METHODS"]
diff --git a/je_auto_control/utils/theme_normalize/theme_normalize.py b/je_auto_control/utils/theme_normalize/theme_normalize.py
new file mode 100644
index 00000000..742d9d67
--- /dev/null
+++ b/je_auto_control/utils/theme_normalize/theme_normalize.py
@@ -0,0 +1,86 @@
+"""Theme-invariant image normalisation so light templates match dark mode.
+
+``match_template`` correlates raw pixel intensities, so a template captured in
+light mode scores terribly against the same control in dark mode — the polarity
+is inverted. The fix is to compare *structure* (edges, gradients), which is the
+same regardless of which way the colours run. ``theme_normalize`` turns an image
+into a polarity-invariant representation before matching:
+
+* :func:`normalize_theme` — map an image to a normalised single-channel image.
+  ``sobel`` (default) and ``laplacian`` use gradient magnitude, which is
+  identical for an image and its inverse; ``zscore`` standardises intensity.
+* :func:`match_theme` — :func:`normalize_theme` both the template and the
+  haystack (the screen by default), then locate the template — finding it across
+  a light/dark theme flip that defeats raw matching.
+
+cv2 / numpy are imported lazily, so importing this module never requires them
+(the package stays importable everywhere) and the locating logic reuses
+:func:`visual_match.match_template`. Imports no ``PySide6``.
+"""
+from typing import Any, Dict, Optional, Sequence
+
+# A normalisation method name.
+THEME_METHODS = ("sobel", "laplacian", "zscore")
+
+
+def _to_uint8(array: Any) -> Any:
+    """Rescale a float array to a 0..255 uint8 image."""
+    import cv2
+    return cv2.normalize(array, None, 0, 255, cv2.NORM_MINMAX).astype("uint8")
+
+
+def _zscore(gray: Any) -> Any:
+    """Standardise intensity to zero mean / unit variance (not inversion-safe)."""
+    import numpy as np
+    std = float(gray.std())
+    if std < 1e-9:
+        return np.zeros_like(gray)
+    return (gray - gray.mean()) / std
+
+
+def normalize_theme(source: Any, *, method: str = "sobel") -> Any:
+    """Return ``source`` as a theme-normalised single-channel ``uint8`` image.
+
+    ``sobel`` / ``laplacian`` return gradient magnitude — identical for an image
+    and its colour-inverted (dark-mode) twin — and ``zscore`` standardises
+    intensity. Raises ``ValueError`` for an unknown ``method``.
+    """
+    import cv2
+    import numpy as np
+    from je_auto_control.utils.visual_match.visual_match import _to_gray
+    gray = _to_gray(source).astype("float64")
+    if method == "sobel":
+        gx = cv2.Sobel(gray, cv2.CV_64F, 1, 0, ksize=3)
+        gy = cv2.Sobel(gray, cv2.CV_64F, 0, 1, ksize=3)
+        result = np.sqrt(gx * gx + gy * gy)
+    elif method == "laplacian":
+        result = np.abs(cv2.Laplacian(gray, cv2.CV_64F, ksize=3))
+    elif method == "zscore":
+        result = _zscore(gray)
+    else:
+        raise ValueError(f"unknown theme-normalize method: {method!r}")
+    return _to_uint8(result)
+
+
+def match_theme(template: Any, *, haystack: Optional[Any] = None,
+                method: str = "sobel", min_score: float = 0.5,
+                region: Optional[Sequence[int]] = None
+                ) -> Optional[Dict[str, Any]]:
+    """Locate ``template`` in ``haystack`` after theme-normalising both.
+
+    ``haystack`` defaults to a fresh screen grab (optionally clipped to
+    ``region``). Returns ``{x, y, width, height, score}`` for the best match at
+    or above ``min_score``, or ``None``. Robust to a light/dark theme flip that
+    defeats raw :func:`visual_match.match_template`.
+    """
+    from je_auto_control.utils.visual_match import match_template
+    from je_auto_control.utils.visual_match.visual_match import _grab_gray
+    raw_haystack = haystack if haystack is not None else _grab_gray(region)
+    norm_template = normalize_theme(template, method=method)
+    norm_haystack = normalize_theme(raw_haystack, method=method)
+    match = match_template(norm_template, haystack=norm_haystack,
+                           min_score=float(min_score))
+    if match is None:
+        return None
+    return {"x": match.x, "y": match.y, "width": match.width,
+            "height": match.height, "score": round(float(match.score), 4)}
diff --git a/test/unit_test/headless/test_theme_normalize_batch.py b/test/unit_test/headless/test_theme_normalize_batch.py
new file mode 100644
index 00000000..10174c38
--- /dev/null
+++ b/test/unit_test/headless/test_theme_normalize_batch.py
@@ -0,0 +1,72 @@
+"""Headless tests for theme_normalize (cv2 behaviour + cv2-free wiring)."""
+import pytest
+
+import je_auto_control as ac
+from je_auto_control.utils.theme_normalize import match_theme, normalize_theme
+
+
+# --- cv2 behaviour (gated per-function so wiring still runs without cv2) ---
+
+def test_normalize_theme_polarity_invariant():
+    np = pytest.importorskip("numpy")
+    pytest.importorskip("cv2")
+    rng = np.random.default_rng(0)
+    image = rng.integers(0, 256, (60, 80)).astype("uint8")
+    light = normalize_theme(image, method="sobel")
+    dark = normalize_theme(255 - image, method="sobel")
+    assert light.shape == image.shape
+    # gradient magnitude is identical for an image and its colour inverse
+    assert np.array_equal(light, dark)
+
+
+def test_normalize_theme_zscore_shape():
+    np = pytest.importorskip("numpy")
+    pytest.importorskip("cv2")
+    rng = np.random.default_rng(1)
+    image = rng.integers(0, 256, (40, 40)).astype("uint8")
+    out = normalize_theme(image, method="zscore")
+    assert out.shape == image.shape
+    assert out.dtype == np.uint8
+
+
+def test_normalize_theme_unknown_method_raises():
+    np = pytest.importorskip("numpy")
+    pytest.importorskip("cv2")
+    image = np.zeros((10, 10), dtype="uint8")
+    with pytest.raises(ValueError):
+        normalize_theme(image, method="bogus")
+
+
+def test_match_theme_finds_template_across_inversion():
+    np = pytest.importorskip("numpy")
+    pytest.importorskip("cv2")
+    haystack = np.full((100, 120), 128, dtype="uint8")
+    template = np.full((20, 20), 220, dtype="uint8")
+    template[5:15, 5:15] = 40            # internal edge structure
+    haystack[30:50, 40:60] = template    # place at x=40, y=30
+    dark_haystack = 255 - haystack       # dark-mode: colours inverted
+    result = match_theme(template, haystack=dark_haystack, method="sobel",
+                         min_score=0.3)
+    assert result is not None
+    assert abs(result["x"] - 40) <= 5
+    assert abs(result["y"] - 30) <= 5
+
+
+# --- wiring (cv2-free: the module imports cv2 lazily) ----------------------
+
+def test_wiring():
+    known = set(ac.executor.known_commands())
+    assert "AC_match_theme" in known
+    from je_auto_control.utils.mcp_server.tools import (
+        build_default_tool_registry,
+    )
+    names = {t.name for t in build_default_tool_registry()}
+    assert "ac_match_theme" in names
+    from je_auto_control.gui.script_builder.command_schema import _build_specs
+    specs = {s.command for s in _build_specs()}
+    assert "AC_match_theme" in specs
+
+
+def test_facade_exports():
+    for name in ("normalize_theme", "match_theme"):
+        assert hasattr(ac, name) and name in ac.__all__