So that's a new one. Never heard of fever coats. Googling ensued.
Apparently, stressed-out Moms can have fever-babies, resulting in silvery coloring which is usually out-grown over time until their true color sets in. The good news is, it doesn't cause any harm to the kittens. The bad news is... there are now a bunch of stressed-out forum members waiting for lots of pictures over the next few months!
There is a color of cat called "Black Smoke" that is related to the silver gene,. The coat is white at the base of the hairs, and rest of hair is black If it's a longhair the white would be about an inch white, and the cat looks black except when it moves you get glimpses of the white undercoat. With kittens, it's not as distinctive as in the adult cat. Black Smoke is not a breed tho some people say it is; but this coloration can occur in different breeds, such as Persians, Maine Coone, American Shorthair, British Shorthair, Devon Rex, Manx, etc.. As a breeder of Cymrics (Longhair Manx) for many years, I did get a black smoke kitten that I kept as a breeder. Her sire was a black Cymric and her dam was a silver tabby Cymric. She had some very lovely kittens.