This package carefully selects and defines 9 colors for 13 hues each. All
colors with the same suffix number have equal luminance level. Also the
color black is of level 0, and the color white is of level 10. Choosing
any two colors that differ by at least 5 levels as foreground and
background color will give a proper WCAG Color Contrast.

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