It looks like there might have been too much air in your icing and maybe a little too thin. Since it has been colored, the color might not have blended well. Sometimes colors will do better if left to sit overnight so that the color is fully absorbed by the sugar. If it sat out too long, then it might separate. Usually stirring it well will re-incorporate it.
Air bubbles? Can't say no. These were flooded cookies, so the icing was thin. I've done this before, mixed the RI, colored it and flooded cookies, after allowing the RI to sit for a couple of hours, and have never had this mottled effect. The mottling was on every cookie, so something general certainly was at work. Thank you for your input. I'll try not to be in a hurry next time, that's for sure.
It looks to me like too much liquid.
Did you add your color before or after you thinned it to flooding consistency?
You should add color BEFORE thinning with water because the coloring itself adds liquid.
I added the color before thinning the RI, and I really don't think it was too thin. But, I'll try again and see if I can get better results. Thank you very much for your input.