Colour represented as RGB with each component in the range [0..255].
Note - the predefined colours are hidden when importing the
top-level shim module
Wumpus.Core.Colour directly to use them.
PostScript has no support for RGB-alpha and hence does not support transparency. Thus Wumpus in turn cannot support transparency.
RGB colour type
Colours levels are in the range [0..255]
Note - this is the format used by SVG, whereas PostScript uses [0..1].
It is more efficient to prefer SVG here.