I often get on this site just to see what could come of different breedings. A bay is actually a black horse with the agouti modifier that fades the black to the points. If both parents have recessive red the foal could be chestnut/sorrel. If they both only have one copy of agouti and black the foal could be black, and black is dominant so if the foal got a red and a black with no agouti it would be black. If one of the parents happened to be Dun instead of bay and mislabeled, you could get a red dun or a grulla. You're right, to my knowledge if there is a cream gene present it WILL manifest, even the smoky black stud I work with (hidden cream, he's been tested) has a modified coat color, he's more of a steel gray.