Fix ESPHome cold/warm white color temperature read-back (#167972)

homeassistant/components/esphome/light.py

@@ -259,15 +259,18 @@ class EsphomeLight(EsphomeEntity[LightInfo, LightState], LightEntity):
         if (color_temp_k := kwargs.get(ATTR_COLOR_TEMP_KELVIN)) is not None:
             # Do not use kelvin_to_mired here to prevent precision loss
             color_temp_mired = 1_000_000.0 / color_temp_k
+            data["color_temperature"] = color_temp_mired
             if color_temp_modes := _filter_color_modes(
                 color_modes, LightColorCapability.COLOR_TEMPERATURE
             ):
-                data["color_temperature"] = color_temp_mired
                 color_modes = color_temp_modes
             else:
-                # Convert color temperature to explicit cold/warm white
-                # values to avoid ESPHome applying brightness to both
-                # master brightness and white channels (b² effect).
+                # Also send explicit cold/warm white values to avoid
+                # ESPHome applying brightness to both master brightness
+                # and white channels (b² effect). The firmware skips
+                # deriving cwww from color_temperature when the channels
+                # are already set explicitly, but still stores
+                # color_temperature so HA can read it back.
                 data["cold_white"], data["warm_white"] = self._color_temp_to_cold_warm(
                     color_temp_mired
                 )

tests/components/esphome/test_light.py

@@ -1913,6 +1913,7 @@ async def test_only_cold_warm_white_support(
                 key=1,
                 state=True,
                 color_mode=color_modes,
+                color_temperature=pytest.approx(400.0),
                 cold_white=pytest.approx(0.0),
                 warm_white=pytest.approx(1.0),
                 device_id=0,
@@ -1944,6 +1945,7 @@ async def test_only_cold_warm_white_support(
                 state=True,
                 brightness=pytest.approx(0.4980392156862745),
                 color_mode=color_modes,
+                color_temperature=pytest.approx(277.7777777777778),
                 cold_white=pytest.approx(0.9798, abs=1e-3),
                 warm_white=pytest.approx(1.0),
                 device_id=0,
@@ -2008,6 +2010,7 @@ async def test_cold_warm_white_no_mireds_set(
                 key=1,
                 state=True,
                 color_mode=color_modes,
+                color_temperature=pytest.approx(277.7777777777778),
                 cold_white=1.0,
                 warm_white=1.0,
                 device_id=0,