This has been a discussion around the table:

You have a blue and red villain deck. You have blue red characters. If the card does not say anything about playing on a specific color, can you play a red upgrade on a blue character and vice versa. If no... where is the rule? I called my self reading the rules but I cannot see where it is worded to answer this question. Sorry if this sounds elementary, but it just seems like if it does not say it, then it is ok.

Thanks

Yes. Only exceptions are: "Color Only" and Spot a "Color" the latter requiring one of them to be in play

Thank you.