Graphics::Color::RGB represents a Color in the sRGB color space. Individual
color channels are expressed as decimal values from 0 to 1, 0 being a lack of
that color (or opaque in the case of alpha) and 1 being full color (or
transparent in the case of alpha). If no options are provided then new instance
of RGB are opaque white, (that is equivalent to red => 1, green => 1, blue =>
1, alpha => 1).
