I couldn't find that this had been covered before. Anyway, I found that if you have a khaki shirt and wash it with some black socks, bingo it gives it a gray undertone. I'm sure if any of you have had the misfortune of doing a white wash and and a dark piece of clothing clung to your wash you found that everything went gray.
A guy on my airsoft team has an ACU top that is decidedly pink compared to his pants. Someone pointed that out and he claimed that's just how they "fade". His wife having washed it along with bright red clothing apparently hasn't occurred to him.