I've wondered about that too. I had to dye my hair for a play and it was a darkkkk brown, and today my director saw me and asked me if I had dyed it back! I hadn't, but it has just faded so fast. The thing is, I used shampoo for dyed brown hair. And this happens EVERY time I dye it! I want to dye it again, but why should I do that and just waste the money? Is it possible that some hair just doesn't hold dye?