Grey horse names... hmm... I like Winter, that's a good one for a grey horse. Or Jack Frost. I also like Gandalf, as in Gandalf the Grey from The Lord of the Rings. Or Dorian Gray, Foggy (or Foggy Bottom :p), Grey Goose, Ash, Cinder, Smudge, Earl Gray, Stormy, Cumulonimbus, Nimbus for short! ;) Just be creative!
I really like Earl Gray :) Depends on his personality and just how creative you want to be.
"A rider who would trade partnership for obedience
will have to settle for neither."