My Lucy's fur did this as well, and it turned out to be from her vaccines. I thought it was strange, as the black fur was almost perfectly round... but then I remembered that she had had her shots a month or two before and had developed a lump under the exact area that the hair became discolored. But honestly, I'm almost certain that the discolored hair does not HAVE to result from a shot... any sort of damage to the skin or fur (however seemingly minor) can cause this sort of reaction. But don't panic. The hair does eventually grow out to its normal color. As with everything else having to do with this breed... you just have to be patient
