Lilac is one of the rarest coat colors in American bulldogs, characterized by a pale grayish cote with a lilac or purplish hue. It is not one of the AKC-recognized colors for this breed.
One interesting thing to note is that the lilac results from a black coat diluting twice.
It is diluted first by the chocolate of the [bb] gene and second by the blue or [dd] gene. The chocolate gene changes the coat color to brown, and the blue gene gives it a grayish-blue coloration. The blue and brown genes together lead to the purplish or lilac coloration. Besides the body, their nose, eyelids, and paw pads have lilac patches too.