In my experience a Hereford bull on Brangus cows produces about 1 red calf to 10 black ones. I don't have much experience with Brahman x Angus F1 cows, but I'd expect a similar ratio. Hopefully someone with more first hand experience will reply.
We did it a long time ago and I know several around here who do it. Most calves are black with white or mot face. The steers bring good money at the sell barn and the heifers make excellent replacements.