Fact is, you've got chromosomes with all of their associated alleles available to choose from - but those come from mom and dad. You can tell what some of them are by looking at the snakes you're breeding (mom and dad), but they also have god-knows-what in their genes that isn't being expressed in their phenotype (a la heterozygous whatever).

Each animal has chromosomes in a given number of pairs. Each one in a pair reflects half of a given parent's genetic information.

Example: You have 46, 23 from mom, and 23 from dad. Your dad had 46, but the 23 he gave you were more or less randomly chosen from what HE got from his parents, same with the ones your mom gave ya.

Your mom's 23 got together with your dad's 23 and sorted out amongst themselves which genes were dominant enough to be expressed either exclusively or as a compromise with other genes in other places.

Therefore, if you have an animal that is bright shiny brilliant yellow, you know that this gene or collection of genes exist and thus bright shiny babies are a *possible* result of whatever genetic configurations "randomly" result from a pairing. You can increase the odds of bright shiny offspring by offering a mate who also carries an obvious "bright shiny" gene of his own. It's possible that there exists one or more "bright shiny" genes that are more or less recessive that any snake can be secretly carrying but not displaying, but the fact of the matter is: Unless You Can See It (or know what his parents looked like) You're Gambling (with even less favorable odds than breeding two attractive snakes).

Hoping that your browning-out pastel is going to produce unholy brightness in his children is ... optimistic. It is not entirely insane, however, stranger things have happened. Personally I'd rather use such luck to win a small lottery or something and buy the genes i need for my project in the form of visually remarkable snakes