Improve light docs (#906)

docs/core/entity/light.md

@@ -12,26 +12,26 @@ A light entity controls the brightness, hue and saturation color value, white va
 | ---- | ---- | ---- | ----
 | brightness | int | None | Return the brightness of this light between 0..255
 | color_mode | string | None | Return the color mode of the light. Must be present in the `supported_color_modes` property.
-| color_temp | int | None | Return the CT color value in mireds.
+| color_temp | int | None | Return the CT color value in mireds. This property will be copied to the light's state attribute when the light's color mode is set to `COLOR_MODE_COLOR_TEMP` and ignored otherwise.
 | effect | String | None | Return the current effect.
 | effect_list | list | None | Return the list of supported effects.
-| hs_color | tuple | None | Return the hue and saturation color value (float, float).
+| hs_color | tuple | None | Return the hue and saturation color value (float, float). This property will be copied to the light's state attribute when the light's color mode is set to `COLOR_MODE_HS` and ignored otherwise.
 | is_on    | bool | bool  | Returns if the light entity is on or not.  
 | max_mireds | int | int | Return the warmest color_temp that this light supports.
 | min_mireds | int | int | Return the coldest color_temp that this light supports.
-| rgb_color | tuple | None | Return the rgb color value (int, int, int).
+| rgb_color | tuple | None | Return the rgb color value (int, int, int). This property will be copied to the light's state attribute when the light's color mode is set to `COLOR_MODE_COLOR_RGB` and ignored otherwise.
-| rgbw_color | tuple | None | Return the rgbw color value (int, int, int, int).
+| rgbw_color | tuple | None | Return the rgbw color value (int, int, int, int). This property will be copied to the light's state attribute when the light's color mode is set to `COLOR_MODE_COLOR_RGBW` and ignored otherwise.
-| rgbww_color | tuple | None | Return the rgbww color value (int, int, int, int, int).
+| rgbww_color | tuple | None | Return the rgbww color value (int, int, int, int, int). This property will be copied to the light's state attribute when the light's color mode is set to `COLOR_MODE_COLOR_RGBWW` and ignored otherwise.
 | supported_color_modes | list | None | Flag supported color modes.
 | supported_features | int | int | Flag supported features.
 | white_value | int | None | Return the white value of this light between 0..255. This is deprecated and will be removed in Home Assistant 2021.10.
-| xy_color | tuple | None | Return the xy color value (float, float).
+| xy_color | tuple | None | Return the xy color value (float, float). This property will be copied to the light's state attribute when the light's color mode is set to `COLOR_MODE_COLOR_XY` and ignored otherwise.
 
 ## Color Modes
 
 | Constant | Description
 |----------|-----------------------
-| `COLOR_MODE_UNKNOWN` | 
+| `COLOR_MODE_UNKNOWN` | The light's color mode is not known.
 | `COLOR_MODE_ONOFF` | The light can be turned on or off. This mode must be the only supported mode if supported by the light.
 | `COLOR_MODE_BRIGHTNESS` | The light can be dimmed. This mode must be the only supported mode if supported by the light.
 | `COLOR_MODE_COLOR_TEMP` | The light can be dimmed and its color temperature is present in the state.
@@ -41,10 +41,12 @@ A light entity controls the brightness, hue and saturation color value, white va
 | `COLOR_MODE_RGBWW` | The light can be dimmed and its color is present in the state as an (r, g, b, cw, ww) tuple (not normalized for brightness).
 | `COLOR_MODE_XY` | The light can be dimmed and its color is present in the state as an (x, y) tuple (no brightness).
 
-Note that in color modes `COLOR_MODE_RGB`, `COLOR_MODE_RGBW` and `COLOR_MODE_RGBWW` there is brightness information both in the light`s `brightness` property and in the color.
+Note that in color modes `COLOR_MODE_RGB`, `COLOR_MODE_RGBW` and `COLOR_MODE_RGBWW` there is brightness information both in the light's `brightness` property and in the color.
 
 If the light is in mode `COLOR_MODE_HS`, `COLOR_MODE_RGB` or `COLOR_MODE_XY`, the light's state attribute will contain the light's color expressed in `hs`, `rgb` and `xy` color format. Note that information is lost when the light is in mode `COLOR_MODE_RGB` as `hs` and `xy` don't hold brightness information.
 
+If the light is in mode `COLOR_MODE_RGBW` or `COLOR_MODE_RGBWW`, the light's state attribute will contain the light's color expressed in `hs`, `rgb` and `xy` color format. The color conversion is an approximation done by adding the white channels to the color.
+
 ## Support Feature
 
 | Constant | Description
@@ -70,6 +72,19 @@ class MyLightEntity(LightEntity):
         """Turn device on."""
 ```
 
+Note that there's no `color_mode` passed to the `async_turn_on` method, instead only a single color is allowed.
+
+Colors in the service call will be translated before the entity's `async_turn_on` method is called if the light doesn't support the corresponding color mode:
+| Color type   | Translation
+|--------------|-----------------------
+| color_temp | Not translated, will be passed as is even if not supported by the light.
+| hs_color | Will be removed from the service call if not supported and translated to `rgb_color`, `rgbw_color`, `rgbww_color` or `xy_color` if supported by the light.
+| rgb_color | Will be removed from the service call if not supported and translated to `rgbw_color`, `rgbww_color`, `hs_color` or `xy_color` if supported by the light.
+| rgbw_color | Not translated, will be passed as is even if not supported by the light.
+| rgbww_color | Not translated, will be passed as is even if not supported by the light.
+| hs_color | Will be removed from the service call if not supported and translated to `hs_color`, `rgb_color`, `rgbw_color` or `rgbww_color` if supported by the light.
+
+
 ### Turn Off Light Device
 
 ```python