Black and red color scheme, likes guns and motorcycles despite that clashing with the aesthetic of the entire universe he's from, I've literally referred to his Silvally as a failed attempt at creating "the ultimate lifeform" and joked about it being Chaos type. And his background involves performing genetic engineering experiments on himself, Shadow's a genetically engineered hedgehog. And he's got silver hair and his Silvally's got an all-silver color scheme, and Shadow turns all silver when he goes Super Shadow.

He even runs a hail team with fucking Beartic instead of Sandslash-A just because he doesn't like Sandslash-A
HE EVEN HATES THAT DAMN BLUE HEDGEHOG
HOW DID I NOT REALIZE THIS SOONER