The MetaPost format plain.mp provides only five built-in colour
names (variables), all of which are defined in the RGB model:
red, green and blue for the primary colours and black and
white. The package makes more than 500 colour names from
different colour sets in different colour models available to
MetaPost. Colour sets include X11, SVG, DVIPS and xcolor
specifications.

Homepage:
https://ctan.org/pkg/mpcolornames
