I have a GeForce 7600GS
I tried setting the overbrightbits variable to 0 which had an interesting effect. After switching between the two clients it would still cause the way other programs look to change, but the effects were not nearly as bad. It only changed the colors slightly(I can now clearly identify the Forward button); on some programs it is more noticable than others.
Also, I am curious as to whether anyone has tried to recreate this glitch on their own system.
To make it you simply open two clients, go onto a server with each one, and alt-tab between them.