We gave Zoey her first hair cut about a month ago. She had been black as a puppy, and then her fur turned tan/red at the roots and grew out like that.. So when I gave her her first hair cut, all the black tips came off. But now, as it's starting to get longer again, the tips on her back are turning black again!! Is this common?? And why is it happening, or.. more specifically -HOW-?? I thought hair got it's pigment right when it came out at the root?