Thank you for taking the time to reply to me. The strange thing is that the haloing wasn't there right after I sprayed it. Everything looked crisp and clean - especially since I used a piece of silk over the stencil. The haloing appeared later. Not sure how much later since I was working on other cookies, but when I went back to them a couple hours later, they looked like this. I guess I do need to let my base icing dry longer, although it happened even when I let it dry overnight. And I need to figure out how not to be heavy-handed. I hold my gun several inches away and feel like I'm only applying light coats, but I must not be. And I also think the fan is making the base too slick.
I see two halos - one that looks like fuzz under the icing (bleeding) and one that looks like under-sprayed speckles (from too low-pressure on the compressor), but if both appeared later, then both are bleeding, I suppose. Hard to say without being there. However, I airbrush and stencil a lot, and I've never had a dark color bleed into my icing, but I am always sure that my icing is set all the way through. I also quick-set my icing in front of a dehydrator, so it has a slick, satin sheen. That being said, I don't think drying in front of the fan is an issue, unless you're drying wet coloring on top of wet (partially dry) icing in front of the fan.