I've had her for two months, and the prior owner had her for three (and the one before that showed us pictures of her as a foal; they didn't care for their animals, but they did take pictures), and we have not noticed any graying, although I won't say it isn't a possibility. She's young, and things change.
The best anyone could think of, is a gray or blue roan.
Whatever she is, color doesn't matter to me (although I'd like it if she stayed dark, as light horses look dirty too easily!).
RMH seems like a possiblity, as they're incredibly popular here.