I'm trying but I can't figure out how "to point my x server to rgb.txt"
in /etc/X11/xorg.conf:
Section "Files" RgbPath "/usr/share/X11/rgb" EndSection
should fix it (locate rgb.txt first, and note theres no '.txt' in rgbpath). i had the same problem (pd wouldn't start due to missing color) after upgrading xorg but keeping the old conf file which had a bad path to the rgb file, but who knows, maybe your problem has a different source (really outside of pd or tk's ballpark either way)
what do you mean?
your default RGB colors arent getting defined.