I’ve colored entire tiers with my airbrush, but if you need to keep going over it, it might make your fondant too wet. If you decide to airbrush the tiers, I’d wait until the fondant has had time to settle.
Having said that, my advice would be to purchase black and red fondant – I wouldn’t take a chance with a wedding cake. I agree with Cakesbylala – Wilton works better than Satin Ice, which tends to be too soft. I know most bakers think that Wilton’s fondant doesn’t taste good, but iI don’t find it that bad – I use it when I need better coverage on my cakes, or when I need a deep color. Keep in mind that most people eat the cake and leave the fondant on their plates – could it be because it’s Wilton’s?? LOL