I've got frustrated of not being able to find 16 colors well distinct of each others, so I added an option to force only 8 colors to be used. So with this option you could only define the 8 first colors, and they will also always appear in order.
customcolors.zip@Seleucids
For the mod above, there are no default config, boolean options are bugged, check and uncheck to actually set to false
Or here is the configuration I'll set as default for ModernGUI with a good color palette that is nice for any game size from 1v1 to 4v4. (That config can be used for Mentula's original version as well ofc, I kept them cross-compatible).