Represents 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.