I really love a good holographic polish :) One that's black and one coat is awesome as well. This is BK 20 and I actually used two thin coats (you could get opacity in one if you want). The one thing I love most about this polish is that it has diamond dust in it so it has much more holo-y goodness. The linear holo rainbow is strong on this polish, you can see it has blue, green, red/orange, yellow. I added SV as a top coat and you can see it didn't dull the effect. I've actually never had a holo that's been dulled by a top coat. This polish came from Hong Kong in a swap I did but I hear if you search hard enough you can find it in the U.S. now (by search I mean the internet, not in stores).
Happy Birthday again to Harri and thanks for letting me invade your blog today :)
Thank you Kristin for making me realize I need a black holo. AND that I'm getting older tomorrow :p