Aftermarket plastic kits

Hey guys, I got a question about black plastic kits...I saw a guy selling a yz250, and he claims that he put a black plastic kit on it. But when I look at the pictures of the bike, there are some scratches on the plastics, but the scratches reveal some kind of a purplish color. Is this normal?? It can't be the original plastics , because he showed them to me.

Any Help will be appreciated!!