I have not even worked with fondant yet, but my wheels are turning.
Can you color fondant with an air brush machine or is it better to just add the color and knead it in yourself?
I don't know if something is better but I normally just knead the color in, goes really well.
About the airbrush I can't help you, don't have one but I have seen a lot of cakes with fondant with airbrush, but it seems to me that you use it as a highlight of to add some color on for example RI decorations (like swirls etc).
Good luck with your attempts, I only work with fondant and I think it's absolutely great stuff!! 
Lara
You can use either method to color fondant. For most colors, I just knead the gel colors into the fondant. For dark colors (black and red especially), if I do not have a store-bought colored fondant, I prefer airbrushing as it takes a lot (and I mean a lot) of gel colors to achieve the deep colors.
Okay, I finally got an airbrush, and I'm very excited about using it. The only problem is, I don't know if I have to buy special airbrush color, or can I mix gel and vodka to spray it on? Sorry to hijack, but I'd really like to know!
Christie 
Okay, I finally got an airbrush, and I'm very excited about using it. The only problem is, I don't know if I have to buy special , or can I mix gel and vodka to spray it on? Sorry to hijack, but I'd really like to know!
Christie
I've read other people had success using gel colors and vodka with their airbrushes. I'd be leary to do this myself, in fear of clogging the airbrush. There are water based colors that are meant for use in airbrushes, like these by Americolor from CC: http://shop.cakecentral.com/amerimist-brush-colors-p-1669.html
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