It's more complicated than that having worked with all three. Cumberlands tend to have broder stripes on the head, and with age, tend to get darker than RES. A RESxYellowbellied can look like a cumberland (by chance). Genetically, its traits are not stable. Mated with another cross, you could have a RES, Yellowbelied, cumberland, or something wierd. Cumberland with a cumberland produces cumberland because of the stablility in its genetic heritage. I would content that it is a hypbrid as its stripe has a redish tent, most cumberland stripes are yellow, or yellow-green.
:A cumberland slider looks like a red-ear with yellow or really yellowish orange instead. This one is definitely a YellowbellyXRES