Now that many of us will acquire new characters from shards before getting cover pulls, we theoretically have a lot more control over the color of our token covers. But that also means we have to choose. So for the newer releases, here are my thoughts:
Immortal Hulk: Green, a thousand times green!
Havok: blue
Sinister: ? Purple or blue?
BRB: blue
Carnage: black for the extra turns?
Professor X: blue for the passive damage and boardshake
Iceman: blue for the stun
Storm: black for the free charge tiles?