It's really neat-looking in the bottle because it's a crazy copper/orange fine glitter mixed with a bunch of fine silver holo glitter. Outside, the bottle looks like the base turns black while you can still see both colors of glitter. On the nail it turns out to be a bit less spectacular, but still pretty awesome. I tried the first nail (my index) with Trick-or-Treat on its own, and it's a little "dirty" looking, so I decided to try layering it over other colors (2 coats layered on each color, 3 coats on its own). Shown below are Trick-or Treat over (thumb to pinkie) China Glaze Marmalade, by itself, Essence Get the Fever, Barielle Make it a Latte, and Wet'n'Wild Black Creme.
Del Sol Trick-or-Treat (shade)
Del Sol Trick-or-Treat (sun)
Overall, I think I like it over brown the best because it complements the copper color of the glitter, and it looks like a deep rich black in the sun, although the oranges look pretty awesome too! Over the orange, it turned more of a deep, dark plum purple instead of black.
As far as I know, it may be hard to find this one in Walgreens, but most Del Sol storefronts should have it available. If you don't live near a Del Sol store, you can order it online at http://www.delsol.com/, but I'm not sure about their international shipping policy.
So what do you think? Do you like the cool color changes of Del Sol Trick-or-Treat?