Looking at the picture that Hair posted, it looks like he may be. To be a bay, his points (legs, mane, tail) would be black where they aren't white.
His tail used to be mostly black. As Hair says, he may be bleached. He has black in his mane and if you wanted to be picky there is actually 4 different colors to his mane because he has a light and darker blond/white. He has some black on his legs but it isn't solid.