Actually, winter coats are far more reliable than summer coats for figuring out colour when it comes to bay vs brown at least.
I actually have a standardbred who I was convinced was bay. I think it may have been NdAppy and/or Chiila who originally suggested that in all likelihood he was brown. I didn't believe it to begin with, but after watching him go through a few more sheds I have come to the conclusion that, yep, he's brown. So welcome to the bad ass brown club Phoenix!
And also a couple of more recent ones of Romance