I'm fine with both the X2 and X3 designs for Colossus.
I think people tend to whine about things that don't matter and aren't accurate complaints, like Colossus' bluish tint in X2 VS his more silver shine in X3, which I put down to lighting in that particular sequence more than anything about the character himself.
When you look at this design, I realize that it may not just be a design change from film to film, but there could even be a subtle sense that his power and his control over it is evolving from film to film.
In X2, he's sort of like metal musculature. Sort of a very basic Colossus.
In X3, he's kind of also the musculature, but an argument could be made that he's also more armored in general, the striations are somewhat fainter, and given that his hair solidifies.
Here, it almost looks like he's actually able to create metal skin over that musculature, not just metal musculature, and that he may be even more armored. Perhaps he's learned to control his powers and to armor not just his muscles, but his skin itself, his eyes, his hair, and even to create actual layered "battle armor" on himself, hence the arm rings.