A `GdkRGBA` is used to represent a color, in a way that is compatible with cairo’s notion of color.
`GdkRGBA` is a convenient way to pass colors around. It’s based on cairo’s way to deal with colors and mirrors its behavior. All
values are in the range from 0.0 to 1.0 inclusive. So the color (0.0, 0.0, 0.0, 0.0) represents transparent black and (1.0, 1.0, 1.0, 1.0)
is opaque white. Other values will be clamped to this range when drawing.
Returns a textual specification of this
in the form `rgb(r,g,b)` or `rgba(r,g,b,a)`, where “r”, “g”, “b” and “a” represent the red, green, blue and
alpha values respectively.