diff --git a/homeassistant/components/cync/light.py b/homeassistant/components/cync/light.py
index b53a78a842a4..5a18d4a4b0f0 100644
--- a/homeassistant/components/cync/light.py
+++ b/homeassistant/components/cync/light.py
@@ -58,6 +58,7 @@ class CyncLightEntity(CyncBaseEntity, LightEntity):
     """Representation of a Cync light."""
 
     _attr_color_mode = ColorMode.ONOFF
+    _attr_supported_color_modes: set[ColorMode]
     _attr_min_color_temp_kelvin = 2000
     _attr_max_color_temp_kelvin = 7000
     _attr_translation_key = "light"
@@ -129,10 +130,12 @@ class CyncLightEntity(CyncBaseEntity, LightEntity):
             and self._device.color_mode == 254
         ):
             return ColorMode.RGB
-        if self._device.supports_capability(CyncCapability.DIMMING):
+        if ColorMode.BRIGHTNESS in self._attr_supported_color_modes:
             return ColorMode.BRIGHTNESS
+        if ColorMode.ONOFF in self._attr_supported_color_modes:
+            return ColorMode.ONOFF
 
-        return ColorMode.ONOFF
+        return ColorMode.UNKNOWN
 
     @override
     async def async_turn_on(self, **kwargs: Any) -> None:
diff --git a/tests/components/cync/test_light.py b/tests/components/cync/test_light.py
index aabf9e072289..e5a716e98371 100644
--- a/tests/components/cync/test_light.py
+++ b/tests/components/cync/test_light.py
@@ -1,10 +1,13 @@
 """Tests for the Cync integration light platform."""
 
-from unittest.mock import AsyncMock
+from unittest.mock import AsyncMock, PropertyMock, patch
 
+from pycync import CyncLight
+from pycync.devices.capabilities import CyncCapability
 import pytest
 from syrupy.assertion import SnapshotAssertion
 
+from homeassistant.components.light import ColorMode
 from homeassistant.core import HomeAssistant
 from homeassistant.helpers import entity_registry as er
 
@@ -71,3 +74,80 @@ async def test_turn_on(
     test_device.set_combo.assert_called_once_with(
         True, expected_brightness, expected_color_temp, expected_rgb
     )
+
+
+@pytest.mark.parametrize(
+    ("capabilities", "expected_fallback"),
+    [
+        pytest.param(
+            {
+                CyncCapability.ON_OFF,
+                CyncCapability.DIMMING,
+                CyncCapability.CCT_COLOR,
+                CyncCapability.RGB_COLOR,
+            },
+            ColorMode.UNKNOWN,
+            id="full-color",
+        ),
+        pytest.param(
+            {CyncCapability.ON_OFF, CyncCapability.DIMMING, CyncCapability.CCT_COLOR},
+            ColorMode.UNKNOWN,
+            id="color-temperature",
+        ),
+        pytest.param(
+            {CyncCapability.ON_OFF, CyncCapability.DIMMING, CyncCapability.RGB_COLOR},
+            ColorMode.UNKNOWN,
+            id="rgb",
+        ),
+        pytest.param(
+            {CyncCapability.ON_OFF, CyncCapability.DIMMING},
+            ColorMode.BRIGHTNESS,
+            id="dimmer",
+        ),
+        pytest.param({CyncCapability.ON_OFF}, ColorMode.ONOFF, id="on-off"),
+    ],
+)
+@pytest.mark.parametrize("device_mode", [0, 101, 253, 255])
+async def test_unrecognized_color_mode(
+    hass: HomeAssistant,
+    mock_config_entry: MockConfigEntry,
+    capabilities: set[CyncCapability],
+    expected_fallback: ColorMode,
+    device_mode: int,
+) -> None:
+    """Unrecognized device modes must not produce an invalid light state."""
+    with (
+        patch.object(
+            CyncLight, "supports_capability", side_effect=capabilities.__contains__
+        ),
+        patch.object(
+            CyncLight, "color_mode", new_callable=PropertyMock, return_value=device_mode
+        ),
+    ):
+        await setup_integration(hass, mock_config_entry)
+
+        state = hass.states.get("light.bedroom_bedroom_lamp")
+        assert state.state == "on"
+        assert state.attributes["color_mode"] == expected_fallback
+        assert "white" not in state.attributes["supported_color_modes"]
+
+
+@pytest.mark.parametrize(
+    ("device_mode", "expected_mode"),
+    [(1, ColorMode.COLOR_TEMP), (100, ColorMode.COLOR_TEMP), (254, ColorMode.RGB)],
+)
+async def test_recognized_color_mode(
+    hass: HomeAssistant,
+    mock_config_entry: MockConfigEntry,
+    device_mode: int,
+    expected_mode: ColorMode,
+) -> None:
+    """Recognized temperature and RGB modes retain their existing mapping."""
+    with patch.object(
+        CyncLight, "color_mode", new_callable=PropertyMock, return_value=device_mode
+    ):
+        await setup_integration(hass, mock_config_entry)
+
+        state = hass.states.get("light.bedroom_bedroom_lamp")
+        assert state.state == "on"
+        assert state.attributes["color_mode"] == expected_mode