Its a piebald deer. the color change comes from a different pigment change in the skin cells making the skin and hair two toned colors; brown and then the white which is no pigment. There are also albino deer(no pigment), white deer (white pigment- the difference from albino is the hooves,eyes and nose on a white deer are black instead of pink) and then Menanism, which is a black deer where there is too much pigment causing them to darken or be black!