Darker Coat and Nibbling on Blankets

I'm posting this because Mommy is making me post this:

Does anyone else notice their shiba's coat darkens in the winter and lightens in the summer? When we got Mika last year during the winter, he was as dark as he is now, but during the summer, he lightened out (picture with rawhide and tennis bone toy [taken in July]), and now he's getting darker again (picture that looks like Mika is eating the snowman blanket [taken in January]). He is like the opposite of humans, we tan because of more exposure to sunlight during the summer, and get lighter during the winter because of less exposure to sunlight. How odd... Could this be because of his diet? He is now eating Canidae beef and fish dog food which is higher in protein. When the July picture was taken he was eating Beneful. But when we changed him from Beneful to Royal Canin (which he didn't like... so picky.. this dog likes beef and lamb. He doesn't care much for chicken.) his coat color didn't really change.. it stayed the same as when he was on Beneful, so that rules out food, right? Let me try to find a picture where his "shoulder patches" are showing. His shoulders are the same color as he was during the summer, but most of the rest of him is darkening. You can kind of see his shoulder patch on the picture below. There is a patch of fur that is lighter near his back (color goes dark-light-dark). Looking at pictures of when we first got him, he has always had that "shoulder patch," but now since he's darker, it has made me notice it more.

Any does anyone else's dog like to nibble on down blankets or cloth in general (as I try to show in the picture with Mika looking like he is eating the snowman blanket)? We brought this habit up with the vet and they don't know what is causing his nibbling habit. The vet's guess is that he is itchy and that by chewing on the cloth, he is imagining chewing on himself? (Sounds kind of out there to me.) He seems to prefer nibbling on blankets, his bed, or cloth (only light cloth like t-shirt jersey, not jeans, sweatshirts, socks, and fleece) that is in front of him over chewing on rawhide.