I find that AmeriColor pops pretty well, as long as you get enough on the cookie. But, I do get shinier results by mixing my own coloring using powdered coloring (luster dust) and vodka. This can be tricky though, as you need to mix it in the exact right ratio so as not to clog your airbrush or get the cookie too wet (with too-liquid coloring). I usually mix in a ratio of 1:4 (powder:vodka, by volume) and stir and shake well. I use Chef Rubber dusts most often for this, as they are quite shiny and I can get huge quantities of it relatively cheaply.