Hi, has anyone come across the instructions on how to air brush chalkboard effect on cookies?

just royal or fondant would do it without airbrushing -- which part do you want to airbrush? there's loads of you tube tutorials

http://www.cakecentral.com/tutorial/45255/chalkboard-cupcake-toppers

The solid black color.  Does black royal icing turn teeth black?  The airbrush black color I have is kind of looking green to me.

yes it's a little creepy on the teeth