I can't see why there would be a difference between white and colored shirts, but you never know!
We double hit our foil, no flash, but two print strokes, then it goes through the conveyor dryer for cure (a little lower temp than normal prints) then to the heat press for foil application. We actually take the extra step to set the foil post heat press - we run them through the conveyor again which ensures the foil is cured correctly and will not wash off.