Well, if you are looking into buying a frosted I would definately ask each and every breeder that sells corns under that name exacty what makes up thier frosteds. Frosting can be a selectively bred trait in pure corns. However, I have seen a few different "frosted corns" sold that are hybrids. I have a pair of snakes that I bought as "Rusty Frosted Corns" along with the full disclosure that they were Grey Rat X Hypo Corn F3's. Funny thing is, they don't even look frosted to me.
Even on Don S.'s website, he sells a "Frosted Creamsicle". Most people know Creamsicles are intergrades (and most assume emoryi is used), but if you note the scientific name... it says that it is a Corn X Grey Rat Hybrid. It is another one of those names that has been used for two different things so you'll have to ask each breeder whether his or hers are line bred corns or hybrids.