I used Krylon Fusion paint.I Inflated a tube inside the tire without the rim,to stretch the tire.Left the tube in,masked the tire portion off that i didnt want white.Sprayed the tire with plenty off light coats over about 30 minutes.let it dry 24 hrs.,lightly went over it next day lightly with a grey 3M pad,wipe clean with water,let dry.Repeat lightly spraying with Fusion to fill in any cracks or chips.Thats about it.You can put your own spin on the technique.Hope it helps.
P.S.-same thing works on changing white walls into colored walls.
Thanks.
-Kreep-