How do i prevent my fallout 2 and fallout 1 game from having rainbow colors?

I have Fallout classic collection and im playing the fallout 1 1.3.4 and fallout 2 1.02.25 please help.

i tryed alt tab so didn't leave any answers about that. thanks.How do i prevent my fallout 2 and fallout 1 game from having rainbow colors?
You have to set your resolution quite low.