I had asked a question about making your own colors for an airbrush and was told not to because it could clog the airbrush. But I just tried using gel color and vodka (like luster dust and vodka) and it did work, but then some of the color starting spraying out in blotches of the color. So the gel doesn't completely soak in to the vodka. I would imagine it would be the same with water.

Has anyone ever tried making their own airbrush colors with success?

I would love to know this technique.

I definitively go with airbrush because (personally) I think it's not very yummy to eat black frosting plus sometimes depending on the heat it will bleed, besides airbrushed black will take less of your time than coloring your frosting but be really careful when transporting the cake if it touches anything you will end up with a white hole in your cake!.
Now to be honest with you I always buy my airbrush colors, its faster, won't clog your airbrush and you always get the same shade of color. There, I hope it helps.