I can think of three really good reasons why Pietro's hair should be a normal colour and not white like in the comics.
1. Pietro inherited his hair from his dad, Papa Magneto. In the X-men series, Magneto's hair is caused by age and as we saw he either had brown or black hair when he was younger.
2. He can't mention ol' Daddy Magneto anyway so you don't need that visual link
3. It might make him look old and grey.
That said, I would love to see Pietro's hair colour just like in the comics for some even better reasons...
1. It's always good to follow what the comics have done to a certain extent
2. It's cute. Trust me, if fangirls made Avengers 2 a hit because of Loki (some of them anyway) then they will LOVE Pietro!
3. It defines Pietro's oddness and gives him an alternative punch-to-the-status-quo look. Somewhere around David Bowie or Spike from Buffy (which alot of people have been comparing him with)
What do you think?
Here is what they might go for...
(Just kidding about the last one
). I reckon the first one would suit Pietro the best. It's intriguing and matches his personality.