Forgive the silly question, but are you certain the file you're testing with actually references the colour value you are modifying?
The colour values are fetched from the colors.txt - the PDMS_colors.txt is a template that could be renamed to colors.txt if you wanted the PDMS standard colour scheme.
If, for example, the file refers to a colour value of 50, this is mapped to Wheat, which is mapped to 96,87,70 (RVM colour values go from 0-100). If you wanted a different resulting colour for Wheat, you'd change the entries to, say, 30,30,30 for a dark grey.
I hope that helps,
Jeff
Senior Software Engineer
Navisworks
Autodesk Ltd.