How to create & use a personal rgb.txt

Greetings --

I'm curious as to an effective way for a user (not root) to set-up a supplemental rgb.txt file for personal use on an X11 system. It's easy
to set up the rgb.txt file (with only new colors) in my directory, but
how can I use it in addition to the standard rgb.txt file.

Thanks.
++ Slapshot_Paulie