The following is an extract from the old newsgroup where @pascal explains how to customise the color dialog. Its a good idea to save the default file as a back-up in case you want to return to the original and I’m not sure if your custom file will be over written during updates.
This extract is for V4, V5 has changed the file name from colors_1033.txt to colors.txt and you’ll find it in the support file:
Quote -
To define your own color palette, customize the
colors_.txt file in the Rhino Support folder.
(e.g. colors_1033.txt for English)
If the colors_.txt file contains more than one color
definition, the internal color list is replaced with the colors
extracted from this file.
The “;” or “//” characters can be used as comments either at the
beginning of a line or after the color definition.
MyColorName1,105,105,105
MyColorName2,0,0,0
MyColorName3,255,60,0
End quote
I just tried this and here is a screenshot:
