While it is not simple genetics, I believe yellow in the cream is somewhat dominant and difficult to breed out if it is there. The yellow is not often present when they hatch, but can become vivid in a matter of a few sheds.
Putting a cal king that visually looks like it has white bands next to one that really has white bands often reveals the yellow in the bands.
I've also noticed that light effects how visual the yellow is - and I have one cal king that changes color to some degree - not a fast change, but sometimes her cream is really yellow and sometimes it is a pale yellow, I'm not sure why.
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11.14 L. getula californiae (Cal. King)
2.3 L. getula nigrita (MBK)
1.0 L. getula floridana (Brooksi)
1.0 Pantherophis guttatus guttatus (Corn)
0.1 Pituophis catenifer catenifer (Pacific gopher)
4.2 Elgaria multicarinata multicarinata - 14 eggs (Cal. Alligator Lizard)