The BEW is unusual among the self varieties in that it’s actually a marked rat – but with such extreme white markings that the only remnants of colour are the dark eyes. Think of it as a capped with a very tiny cap rather than a pink eyed white with dark eyes.
Black eyed white rats can suffer a whole host of issues. Sadly, the majority of black eyed white rats are deaf, and many suffer from epilepsy too. This is an integral part of the variety as the deafness and epilepsy are just inevitable once the rat is so extremely marked. Attempts were made to breed out the problems that the BEWs have, but the NFRS finally banned BEWs from exhibition in 2010.
Genetics: HeHe, selectively bred for as much white as possible. The rat must also be a dark eyed colour to begin with (so black, agouti, mink, blue, etc).
NFRS Standard: To be as white as possible, devoid of any creamy tinge or staining. Any coloured hairs to be severely penalised. Eyes black.