Passing on Color

I have a blue roan heifer that is out of a RED AND WHITE bull and a BLUE ROAN cow. This does not seem to be too difficult to understand for me, but I am being told by someone that this is impossible and that the bull must be a ROAN, which he is not. Their explanation is that the calf gets her black from the dam and therefore must get the roan from the bull, but I see it as getting the blue and roan genes from the dam's side. Is the roan gene not recessive anyway? I did not think you had to have a roan animal to have a roan calf. How many others have had Blue roans out of red and white bulls?

My neighbor used a blue roan bull. He was sired by a black chi, and out of a blue roan half shorthorn cow. He threw lots of blue roan calves from angus cows. He saved some of those blue roan heifers, bred them black, and they have thrown some blue calves. The red and white bull should make no difference at all on blue cows. Some of the calves could be red, and some will be blue.