Pastel is a co-dominant morph. Co-dom morphs are kind of like enhancements to other genes; they're visual and can make some really cool stuff when combined with dominant and other co-dom genes, but are somewhat subtle on their own.
Het means heterozygous, which is like a hidden gene. It will only be visual if bred to an animal heterozygous for the same thing, or a snake that is already a visual of that gene.
That's an incredibly simplified answer, lol. It can get way more convoluted when you really dive into what gene goes with what, and what genes make supers, etc.
If you want to have fun with possible breeding outcomes and whatnot, there are some morph calculators out there that give you percentages of outcome.
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