Please post a picture of the bull. My bet is that he is black with a blaze face. He is also a red gene carrier. If he doesn't have a white face, then that red cow with horns got bred by the neighbors bull. If she did, then some of the others could have too.
It looks to me like he greatly increased the unifomity of the color of your herd, and in one generation. He at least made them solid. Don't blame the crossbred bull, blame the lack of uniformity in you cow herd.
Your cows are what is causing the color problems, not the bull. If the bull is black, he can't throw the grey color or brown color of that calf on the roan cow, that came from her, not him. If he is black, then he doesn't carry those dilutions genes, they have to come from the cow. A solid black animal doesn't carry the dilution genes. That grey calf on the roan has black hide, therefore the grey diluter is coming from the cow, not the bull.
Next year, you will have mostly black calves from your Angus bull, but also a few greys, so I don't know what you'll be gaining other than less red, they will still be black and grey, just not black, and grey and red. Of course, you'll get rid of the whitefaces too, since the Angus is solid colored.
It's not the crossbred bulls fault, it is just the genetic combination you bought. He's got a gene for black, a gene for red, a gene for no white face, and a gene for whiteface. He's probably heterozygous polled, too. I've used and continue to use crossbred's that sire more uniformity than straightbreds. You just need to educate yourself about how simple traits are inherited.
mtnman