I believe her sire is also bay. (the filly is not mine)
She was born this color and hasn't changed any. The tail was always a mixture of black and white. There is no white flecking on her face, just on her sides and on her chest.
The owner wanted to register her with the AAHA as roan, but roan is not a recognized color in Arabians and consequently the AAHA registered her as bay.
Her coloring has always intrigued me.