The trait is simple recessive just like amelanism.
There were traditionally two strains: the JD strain and JR strain. I can never seem to keep them straight. One strain produces a very light brownish lavender color and nice yellow bands. The other strain produces snakes that are just slightly more pinkish/lavender than a normal amelanistic with very faint yellowish bands. The two strains are not compatible genetically - that is, breed one of each together and you get normal-looking Cal kings.
I like the darker ones myself, which look like you would imagine a hypomelanistic coastal Cal king to look.
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Mark 