My guess is just like everyone else's. Gray (:
We had a Saddlebred mare who looked just like a Bay. When she got a little bit older she started dappling out. It was weird because she was the color of a Bay but had light faded dapples coming through. We sadly sold her, but since then she has become a Grey (:
The tail is a trait of a Grey. Greys are born black, but as they age, they get lighter and lighter.
Personally I like when they're young. They have grey and still some black but some even look blue. (: