In California you can run your original plates indefinitely, if the car does not leave the state, otherwise new ones must be obtained when returning to CA. They have two tags, one is month of registration, that never changes unless there is a title change, and the year is on the other corner and that is renewed every year.
My Xterra has current white reflective plates with blue text and my 72 Datsun 510 is running its original blue plates with yellow text.