Assume that an incompletely dominant gene controls the feat…

 Assume that an incompletely dominant gene controls the feather color in chickens so that BB produces black, BW produces a slate-gray color called blue, and WW produces asplashed-white.  A second gene on a separate chromosome controls comb shape, with the dominant gene R producing a rose comb and the recessive genes rr producing a single comb. If a pure breeding black, rose-comb chicken is mated with a white, single-comb chicken, what proportion of the offspring will be white, single-comb chickens?