Where are X11 resource files under Leopard?

In going from Tiger to Leopard it appears that the way X11 is initialized has changed. Specifically, I had a customized rgb.txt file in /usr/X11R6/lib/X11/rgb.txt that I used for my xterm. My .xinitrc opens X11 with a number of xterms using several special colors I had defined.

In the past, goping from X->Jaguar->Panther->Tiger, restoring my custom file in /usr/X11R6/lib/X11/rgb.txt worked fine. Now, however, it seems that /usr/X11R6 points to /usr/X11R6/lib/X11 and rgb.txt is no longer used.

How does xterm derive its color list now?