Breeding different species together and breeding different morphs of the same species are two completely different things. If you are interested in milksnake morphs, I would look into honduran milksnake. There is alot of variety with that individual species to work with if you are interested in mixing morphs.
I wouldn't say that all milks have 'same basic adult pattern'. Most have different 'combinations' of the reds, yellows, blacks, and whites. There is variation in pattern to some extent if you start considering band thickness,number of bands, blushing, etc....but most are banded (besides morphs).
Here are a few of my different species of triangulum:
Scarlet King (l.t. elaposoides)
Red Milk(l.t. sysphila)
Pale Milk (l.t. multistrata)
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