Airbrushing red and black

[puzzlegut]

Normally when I've colored my frosting by hand with the gel colors and I want red or black, I mix it into chocolate frosting in order to get the dark colors that I want. I'm wondering if I'm airbrushing red or black onto a cake covered in frosting or fondant, will it work out ok if the frosting/fondant is white, or should it start out as chocolate first?

[cakebaker]

It will cover much quicker if the fondant or icing is colored closer to the final color you want.