Do I Need Special Food Coloring?

Airbrushes are designed to be used with much thinner food coloring than soft gel or gel food coloring. I use and like amerimist airbrush colors made by americolor. However, the ingredients are the same, I think the amerimist colors just have more water in them so they are thinner. You can "water down" your soft gel colors with vodka or another type of alcohol in a small container before putting it in the airbrush. I do this frequently and it usually works pretty well. Some colors tend to be thicker than others and therefore do not thin down as well. I have experienced this problem with gold. You do increase the possibility of clogging your airbrush, which can prevent it from spraying or cause it to spray unevenly. Cleaning the gun with warm water has always solved this problem for me, but it might be a risk you don't want to take as you can easily ruin cookies or potentially damage your airbrush. 

Glad i asked because i was going to try with what i had on hand 

I always use either Chefmaster or Americolor airbrush colors - haven't wanted to risk gunking up my airbrush with soft-gel coloring even if thinned down. So far, so good. However, I find the white airbrush color to be pretty thick; if used straight up, it almost always comes out splotchy for me. So I've taken to thinning it (effectively) by adding other colors to it, or using a little vodka with it.