I am going to use airbrushing on a fondant cake for the first time, and would like recommendations for brand and/or type of food colouring to use. Thanks very much!

Welcome to CC and congratulations on your first post!
I use americolors. Don't forget to post your pics.

do you dilute your colors at all, or use it straight from the bottle?

There is specific colors for Airbrushing that are formulated properly for an airbrush.You should never really use gels or pastes watered down as they will probably clog the airbrush head..That being said many people have tried it that way and said it works fine..I would never risk wrecking my airbrush! Americolor and Chefmaster both put out a great selection of colors and Metallic sheens made for airbrushing..Most online decorating stores sell them!!Don't dilute them...use right out of the bottle!I also like to mix colors to get great shades!! Have Fun..and Welocome to CC!!!


Laurel

Yes, I agree with Kiddiekakes, you never use gels or any other kind of food coloring on your airbrush but the one specially made for it. You can buy the kroma kolors from kopykake and for a nice sheen you can get lucks shimmer airbrush color, they have several different shades and give your cake a beautiful finishing touch. . HTH