I was wondering which colors revert back to basic when you put the pet in the adoption center. The only one I know for sure is Hydrus... Please and thanks!

I think it's just Hydrus. Sometimes if you search up a pet in the pound it'll look Common, but it's still actually colored if you view its lookup.

Yeah I'm pretty sure its just hydrus too. Maybe double-check with special 'zap-only' species etc. but as far as colours, I think it's only hydrus.