first: HOLY COW WHAT A BEAUTIFUL SNAKE!!!
okay now info: in other animals the term for this is called heterochromia. in other animals, it can be inherited or it is the effect of random genetic fun-times. since your snake already exhibits some genetic fun-times (see: paradox markings) i would suspect it comes from that same anomoly.
EDIT: in other animals, this (heterochromia) is common for chimeras. you may have a chimera!!!