My understanding is that there's no state law about college campuses. The UW system has an administrative rule that prohibits unauthorized weapons on UW property under penalty of up to a $500 fine. Private colleges, as any private entity can, may prohibit weapons on their property, but whether they do, I don't know. You'd have to check with each college to see if they have a policy. I'd personally be surprised, and happily, if they don't have a prohibition.