mygui bindings for color and alpha

docs/source/reference/lua-scripting/widgets/image.rst

@@ -20,3 +20,6 @@ Properties
   * - tileV
     - boolean (false)
     - Tile the texture vertically
+  * - color
+    - util.color (1, 1, 1)
+    - Modulate constant color with the color of the image texture.

docs/source/reference/lua-scripting/widgets/widget.rst

@@ -35,6 +35,14 @@ Properties
   * - propagateEvents
     - boolean (true)
     - Allows base widget events to propagate to the widget's parent.
+  * - alpha
+    - number (1.0)
+    - | Set the opacity of the widget and its contents.
+      | If `inheritAlpha` is set to `true`, this becomes the maximum alpha value the widget can take.
+  * - inheritAlpha
+    - boolean (true)
+    - | Modulate `alpha` with parents `alpha`.
+      | If the parent has `inheritAlpha` set to `true`, the value after modulating is passed to the child.
 
 .. TODO: document the mouse pointer property, when API for reading / adding pointer types is available