Why did Kaneki's hair change color? At the start of the series, Kaneki's hair is dark brown, except in the OP, where it we see an image of him with white hair. In episode 11, we see a final scene of Kaneki, his hair having turned white. This turns out to be a preview of things to come, his hair being brown at the start of episode 12.

However, during episode 12, we see a scene, theoretically taking place in Kaneki's mind, or as a hallucination, wherein his hair fades from brown to white.



After this scene, however, this color change seems to manifest in the real world, too. (Kaneki's clothes also seem to invert colors.)

What caused Kaneki's hair (and/or clothes) to change color in the actual real world during this episode?
You should read the manga. His hair turned white because of the stress of being tortured 2 or 3 times everyday for 10+ days. 

The anime is wrong. Why? Because Kaneki's hair didn't change in a moment, in the manga they show us his hair gradually turning white while he also  loses his mind. 





 

They don't explain why the hair turns white or the nails black (also they are not black black, they're more like super dark blood colored), but we can assume that the hair it's because of the Marie Antoinette syndrome, and the nails are because of the constant regeneration. Like I said before the nails are like dark blood colored, they're not pure black, it's like when you hit a finger really hard, and the nail falls off in a time? Well before that, it gets really dark blood colored, Kaneki's are like that. 

I know you posted this a time ago but maybe if you can read it, or other people that has the same doubt will understand.