So I googled and searched on painting directly onto a cake with airbrush colors. Got a (supposedly) High quality food safe paintbrush set. And tested yesterday on a small piece of my fondant. It went on fine and this morning was nice and dried. However, when going to paint on this cake it has been one disaster after another. The brushes I paid a leg for shed bristles like you would not believe. And after I did my fist coat, which went on okay after bristle issues, I left it to dry and came back and the color has separated all over the cake. I don't know what to do. It looks like bubbles ever where. Would mixing the color with alcohol help?? 

AI always mix my food color with vodka or lemon extract, I personally like the lemon extract better! The airbrush colors are just very thin so they can go through the airbrush machine!

Do you think mixing with the extract or alcohol and doing a thin layer will stop the separating?

i use regular gel colors and a little bit of wilton white mixed together. I find that it creates a texture more like paint, and I haven't haD any problems like you describe.