The level of rufus (a modifier) impacts the amount (level) of “red” in the coat and is denoted by a plus (for more) and a minus (for less). Scientific literature estimates it is at least 5 gene pairs (some place it as high as 8 pairs). Modelling it as an additive system of 5 pairs in which each gene can be + (more red) or - (less red) think of the darkest red thrianta to be ++ ++ ++ ++ ++. The less red, the closer to cream. Therefore a fawn colored rabbit could either be a dilute or simply one with low rufus.