Not as what we would call a star, no. Unless there was a strange mutation. On some grays it may seem as if there are dark facial markings, but those are actually just dapples, and will fade over time.
Sorry. Not a great answer, but I've never heard of anything like it, and I'm not entirely sure why it couldn't happen (I'll look into it, though), but am sure I've never heard of it. Again, I apologize.