The rhinestones themselves are black but they have a iridescent coating which makes them have an oil on water look to them, which is quite different. I haven't seen any like this before, usually rhinestones come in plain different colours.
I found using these studs even over a black base looked great.
For these nails I used a couple of different sized rhinestones over a black base;
Nails Inc - New York Noir
These nails were done using three of the medium size rhinestones and two larger ones as a little bit of an accent;
Nails Inc - New York Noir
I wanted to try them over a lighter colour base, as a dotticure accent nail;
Barry M - Matt White
The different size rhinestones mean you can create different looks.
Barry M - Matt White
Revlon - Steel Her Heart
Nails Inc - New York Noir
[item send for reviewing, this doesn't affect my views]