I'd noticed when spawning horses that the "creamy" horse with no markings would not spawn. I spawned somewhere around 400 horses trying to get the variant before using the summon command.

Both commands as followed create a horse with "creamy" coloring and a "white" variant, in which the "white" means a white stripe down it's face and white hocks.

/summon horse ~ ~ ~ {Variant:1}

/summon horse ~ ~ ~ {Variant:257}

The first command should bring up a horse with no markings, but it brings up the one with the white stripe. I'm guessing the texture for the bay horse just got overridden on accident in coding to where the horse with the white stripe is now both datatag 1 and 257.