Milani HD is a silver shimmer holographic. It's very sheer with one coat, which was a slight disappointment as it appears to be opaque from the bottle, but it is fairly opaque with three coats. In between coats, the formula dries quickly, so it's not really a pain to apply. It is a nice layering polish as well. I'm sure it would look great applied over a silver, black, blue, (or any) polish. The holo effect is not bad. Indoors, the color looks like a light silver with fine silver glitter. The holo really pops in bright lighting or the sunlight.
I purchased this polish at CVS for a little under $5.
Do you own any of the Milani Holos? Which is your favorite?