If you only need color in the exposed shotcrete surface, just putting color in the flash coat should be adequate as long as the flash coat is continuous across the entire area. You may want to specify the final “flash” layer to be thicker, perhaps 1/2 in. (12 mm) to 1 in. (25 mm) thick. This would help assure consistent color and still allow the finishers to produce a consistent final texture. As long as the concrete materials are the same in the production, you wouldn’t need to shoot the final layer all in one day. Also, be sure curing methods are the same for the entire area as varying moisture can sometimes affect the early appearance of the coloring, though it usually balances out over time.