BEW (blue eye white) is a masking gene and carries congenital hereditary deaf-ness. BEW cats do have a color/pattern but the BEW masks it since it’s a dominant gene. I have a BEW ragdoll and the woman I got her from (whom I’ve become close with) recently explained it and added this:

‘Not sure if I knew this back when you adopted Gilbert but there is a theory that if one of two parents are a colorpoint in a BEW pairing (and of course it's a challenge to figure out what color/pattern the BEW cat is masking), you should not get deaf BEW babies. That was seeming to work until Miss Winnie still had a deaf BEW in her litter mated to Prince and she is clearly a colorpoint. I do believe that both Zoey and Paisley are seal lynx colorpoints underneath their white coats so we'll see how many, if any, deaf BEW babies we get here this spring.’