Change colors of a GTK application

[Summers_Ed emc com]

Hello,

I have a visual impairment and I need to be able to change the colors of a
GTK app.
I'm running RedHat Linux and GNOME.  I need white text on black background
for 
as much of the window as possible (including menus, tree-like navigator
window, etc).

What is the best way to change the colors of an existing app?

Thanks for any assistance,
Ed 

Pls email me directly at summers_ed emc com