feat: color: add channel properties to color

Add extra properties to the `color` type.
- `red`
- `green`
- `blue`
- `alpha`

docs/reference/src/language/syntax/types.md

@@ -66,6 +66,17 @@ draw the outline.
 CSS Color names are only in scope in expressions of type `color` or `brush`. Otherwise, you can access
 colors from the `Colors` namespace.
 
+### Properties
+
+The following properties are exposed:
+
+- **`red`**
+- **`green`**
+- **`blue`**
+- **`alpha`**
+
+All properties are in the range 0-255.
+
 ### Methods
 
 All colors and brushes define the following methods: