diff --git a/homeassistant/components/light/__init__.py b/homeassistant/components/light/__init__.py
index 5855dbfe1c2..e41ffc75964 100644
--- a/homeassistant/components/light/__init__.py
+++ b/homeassistant/components/light/__init__.py
@@ -779,7 +779,7 @@ class LightEntity(ToggleEntity, cached_properties=CACHED_PROPERTIES_WITH_ATTR_):
 
     entity_description: LightEntityDescription
     _attr_brightness: int | None = None
-    _attr_color_mode: ColorMode = ColorMode.UNKNOWN
+    _attr_color_mode: ColorMode | None = None
     _attr_color_temp_kelvin: int | None = None
     _attr_effect_list: list[str] | None = None
     _attr_effect: str | None = None
@@ -801,7 +801,7 @@ class LightEntity(ToggleEntity, cached_properties=CACHED_PROPERTIES_WITH_ATTR_):
         return self._attr_brightness
 
     @cached_property
-    def color_mode(self) -> ColorMode:
+    def color_mode(self) -> ColorMode | None:
         """Return the color mode of the light."""
         return self._attr_color_mode
 
@@ -1014,6 +1014,10 @@ class LightEntity(ToggleEntity, cached_properties=CACHED_PROPERTIES_WITH_ATTR_):
 
         _is_on = self.is_on
         color_mode = self.color_mode if _is_on else None
+        if _is_on and color_mode is None:
+            raise HomeAssistantError(
+                f"{self.entity_id} ({type(self)}) does not report a color mode"
+            )
 
         effect: str | None = None
         if LightEntityFeature.EFFECT in supported_features:
diff --git a/homeassistant/components/mqtt/light/schema_template.py b/homeassistant/components/mqtt/light/schema_template.py
index 3eaeb89caa5..13b83f082b0 100644
--- a/homeassistant/components/mqtt/light/schema_template.py
+++ b/homeassistant/components/mqtt/light/schema_template.py
@@ -187,6 +187,7 @@ class MqttLightTemplate(MqttEntity, LightEntity, RestoreEntity):
             color_modes.add(ColorMode.HS)
         self._attr_supported_color_modes = filter_supported_color_modes(color_modes)
         self._fixed_color_mode = None
+        self._attr_color_mode = ColorMode.UNKNOWN
         if self.supported_color_modes and len(self.supported_color_modes) == 1:
             self._fixed_color_mode = next(iter(self.supported_color_modes))
             self._attr_color_mode = self._fixed_color_mode
diff --git a/homeassistant/components/openrgb/light.py b/homeassistant/components/openrgb/light.py
index c599ab6c3ed..ce4e47c6fa7 100644
--- a/homeassistant/components/openrgb/light.py
+++ b/homeassistant/components/openrgb/light.py
@@ -158,7 +158,7 @@ class OpenRGBLight(CoordinatorEntity[OpenRGBCoordinator], LightEntity):
         else:
             mode_supports_colors = check_if_mode_supports_color(mode_data)
 
-        color_mode = ColorMode.UNKNOWN
+        color_mode = None
         rgb_color = None
         brightness = None
         on_by_color = True
@@ -194,7 +194,7 @@ class OpenRGBLight(CoordinatorEntity[OpenRGBCoordinator], LightEntity):
             # If Off by color, retain previous color mode to avoid changing the UI
             color_mode = self._attr_color_mode
 
-        if color_mode == ColorMode.UNKNOWN:
+        if color_mode is None:
             # If color mode is still unknown, default to RGB
             color_mode = ColorMode.RGB
 
diff --git a/pylint/plugins/hass_enforce_type_hints.py b/pylint/plugins/hass_enforce_type_hints.py
index 1b920d8c55d..47416da20cc 100644
--- a/pylint/plugins/hass_enforce_type_hints.py
+++ b/pylint/plugins/hass_enforce_type_hints.py
@@ -1837,7 +1837,7 @@ _INHERITANCE_MATCH: dict[str, list[ClassTypeHintMatch]] = {
                 ),
                 TypeHintMatch(
                     function_name="color_mode",
-                    return_type=["ColorMode"],
+                    return_type=["ColorMode", None],
                     mandatory=True,
                 ),
                 TypeHintMatch(
diff --git a/tests/components/light/test_init.py b/tests/components/light/test_init.py
index 1b06c152867..ad8a88d5d97 100644
--- a/tests/components/light/test_init.py
+++ b/tests/components/light/test_init.py
@@ -2353,6 +2353,40 @@ def test_filter_supported_color_modes() -> None:
     assert light.filter_supported_color_modes(supported) == {light.ColorMode.BRIGHTNESS}
 
 
+@pytest.mark.parametrize(
+    ("color_mode", "supported_color_modes", "error_expected"),
+    [
+        (None, {light.ColorMode.ONOFF}, True),
+        (light.ColorMode.ONOFF, {light.ColorMode.ONOFF}, False),
+    ],
+)
+async def test_report_no_color_mode(
+    hass: HomeAssistant,
+    caplog: pytest.LogCaptureFixture,
+    color_mode: str,
+    supported_color_modes: set[str],
+    error_expected: bool,
+) -> None:
+    """Test a light setting no color mode."""
+
+    class MockLightEntityEntity(light.LightEntity):
+        _attr_color_mode = color_mode
+        _attr_is_on = True
+        _attr_supported_features = light.LightEntityFeature.EFFECT
+        _attr_supported_color_modes = supported_color_modes
+
+    entity = MockLightEntityEntity()
+    platform = MockEntityPlatform(hass, domain="test", platform_name="test")
+    await platform.async_add_entities([entity])
+    raised_error = ""
+    try:
+        entity._async_calculate_state()
+    except HomeAssistantError as err:
+        raised_error = str(err)
+    expected_error = "does not report a color mode"
+    assert (expected_error in raised_error) is error_expected
+
+
 @pytest.mark.parametrize(
     ("color_mode", "supported_color_modes", "warning_expected"),
     [