Hi Tony,
When I decorate molds with an airbrush, I spray them all first. Then I take a scraper and scrape the excess coloured cocoa butter off the surface of the molds (and sides, if necessary). It drastically cuts down on the amount of coloured cocoa butter getting into my chocolate. You will still get little bits, but it will be a lot better. I also save the coloured cocoa butter that I scrape off and re-use it for future batches (if there is a significant amount - much more likely if you are making many chocolates).
All the best as you make your chocolates!
Christy