From Leopard Gecko Wiki
The Halloween Masks were first pioneered in the late 90's by Albey Scholl of Albey's Too Cool Reptiles when he began working with an unusual gecko he acquired. After many years of line breeding and proving out the head pattern traits, the project was turned over to Paul Allen of Bright Albino and then to other various breeders, such as Brittney Gougeon of PacHerp, and Ryan Hauser of Retribution Reptiles
Halloween Masks hatch out with dark black patterns on their body and heads and develop into juveniles with extremely bold head patterns and unusual body markings. Their bold traits continue to develop and mature all the way into adulthood. Sometimes they are very dark with lavender around their bold markings and tail. Top quality Halloween Masks will change color from a very dark semi-melanistic coloration to a vibrant yellow/bold coloration depending on their mood, temperature, and other conditions.
Baby Halloween Mask Bold Stripe - Het Radar Eccogeckos