Behaviour for colour format handlers.
Each colour format module (ANSI, Hex, RGB, ARGB, HSL, HSV, CMYK, XTerm256, Atom) implements this behaviour to provide a consistent interface for colour parsing, validation, and conversion to all supported colour spaces.
See Pote.Format.RGB, Pote.Format.Hex, Pote.Format.HSL, etc.
for the built-in implementations.