Umm...looks like a little bandana that he'swearing lol...but...hmm.... I don't think fur coloration meansanything, its just a coincidence that he ended up with a "V" on him.lol.
It's a molt line where the new fur is growingin. It has a tendency to show up moreon the shadedcolors, where it is more noticable. It is different from thetriangle marking at the nape of the neck seen in Agouti or Tanpatterned rabbits.
Mocha has a "V" shape in the same spot all thetime. It gets more noticeable when he molts in the summer though.Mocha's "V" also is very unique in that half of it is an off white andthe other half is a light sort of mocha color. It's really hard tophotograph that because he wont sit still to do it.
If it just appeared I'm assuming pamnock is right and it's a molting line.