Correct me if I'm wrong, but when I got my silver HTC One the guy that helped me said that I could exchange the phone for another model within 30 days. He said the 90 days is only for returns or exchanges of the same exact model of phone. He said if I wanted to exchange for the black model or another phone, it would have to be done within 30 days.
30 days is the time frame for exchanging to a different model. Costco managers can override this as the official Costco policy is 90 days. IF the kiosk says no, just go talk to a Costco manager, they never say no.