Based on the guess you had, sounds like you're more used to working with codominant and/or dominant traits. (?)
With corns so far, the standard is recessive mutations. I don't know of any fully dominant mutations in snakes. The only proven codominant I know of is Tiger in retics. Heh, but then I don't follow morphology in other species, so for all I know corns are the weird exception.
Check out my genetics tutorial for a good refresher. Sounds like you've got a decent grasp, and that should bring it all back to you.