Originally Posted by Poseidon
I haven't had Abby in the summer yet (I got her in September), but then she was very golden with a tonnnn of sheen to her coat. Since her winter coat has come in more and more, she's lost the shininess and just looks dingy. Not quite smutty, because it's not very dark. Just a greyish tinge to her golden coat. It's awkward. Not nearly as drastic as your girl, but that's my two cents.
That's just the winter coat. Hunter goes a dark palomino in the summer but is quite light in the winter. Her horse didn't go the dark color last summer which is what her question is. I agree with diet.