Fire and vanilla, and yellow belly and spark, are examples of allelic mutations. A parent will only supply one allele to its offspring, so it would throw either a fire or vanilla allele, or yellow belly or spark allele, but not both, to its offspring. The other side of the mutation equation will come from the other parent.
Okay so if jumbled these four snakes around to say yellowbelly vanilla and spark fire, shouldn't the same thing happen?