Four channel color representation.
RGBA colors are floating point color representations with color channel values between (0..1). Colors may be initialized from 3 or 4 floating point numbers or a hex string:
RGBA(1.0, 1.0, 1.0) # Alpha defaults to 1.0
RGBA(1.0, 1.0, 0, 0.5)
RGBA("#333")
RGBA("#7F7F7F")
Individual color channels can be accessed by attribute name, or the color object can be treated as a sequence of 4 floats.