How to tint powdered sugar (icing sugar)? I'm looking for a way to tint powdered sugar without wetting it.

I know that there are powdered food colors but I think that part of what activates the color is the fact that they get wet when you add them to an icing or batter.

I'm also afraid that they're so concentrated that, even if I get the color I want, I'll end up dyeing the mouths of the people who eat the cookies/cupcakes/whatever that I dust with the powdered sugar.

Is blending/processing colored sanding sugar and adding a bit of cornstarch an option? Will it ever mimic actual powdered sugar?

Edit: I've tried the above (sanding sugar with cornstarch) and it does not make a good solution.
From my experience coloring regular sugar with ordinary food coloring, drying it, and then crushing it in a mortar yields good results. Be careful to not use too much food coloring though, or it will never dry properly! I haven't tried to see if cornstarch might save it, but as long as you do the drying properly and don't overdo the amount of color it shouldn't be necessary.

As for the powdered food coloring option you suggested, I found a source that said they don't have to be wet to take effect, but it doesn't say anything about whether the eaters will be colored =)