You can let them dry completely and then airbrush them. Or you can mix airbrush color with Everclear or alcohol and dip the flower upside down in the color, spin the flower upside down by the wire stem after dipping to remove excess color, I'd suggest doing that inside a cardboard box because it flies everywhere. Check your flower and see if the color got into all the little cracks, if not just dab the liquid on with a tiny artists paintbrush. Stick the stem into a block of styrofoam to dry. Either way I would color the gumpaste with gel or paste color in a lighter version of the finished color you are looking for.