why do you have the colorRamp definition itself inside a BEGIN {} block?

Just to ensure that the lookup table is built before the sub can be called.

That would take care of itself if it was in a module. But so far, everyone who's contacted me about the snippet has had a different set of requirements of it. Some want discrete rgbs; some rgba; some as html-style 3 or 6 hex digits; some want cmyk. Everyone seems to need to adapt it some way or another.