Good suggestions from Jimmy and Doug, above.

Also, there are a couple Old World species which have several morphs each.

Steppes Ratsnake (Elaphe dione) has several morphs, phases, and locales - although most of them have yet to make it to the U.S.

Chinese Beauty Snake (Orthriophis taeniurus taeniurus) also has several morphs, a few of which are available in the U.S.
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-Toby Brock
Southwestern Center for Herpetological Research