Pink Cosmo is one of the Fall 2012 limited edition Maybelline Color Show polishes. It's a greenish-gold/rosy-pink duochrome shimmer. It's on the sheer side; I used three coats and still can see some visible nail line.
The shift in this is subtle; below you can see its golden face on the left shading to its pink face on the right (proof that moving one's fingers around while taking dozens of shots does work out sometimes).
Sunlight does not do this polish many favors. It does bring out more sparkle, true, but at least on me, it also makes my nails look sort of dirty.
Because this is a) sheer and b) a duochrome, I had to try layering it. I left the three coats of Pink Cosmo alone on my index finger (top in photo below), then put one coat over (moving from top to bottom) Essie In Stitches, OPI Uh Oh Roll Down the Windows, and Wet 'n' Wild Black Creme.
Not surprisingly, the pink/green shift was most obvious over the black, with the green/gold in Pink Cosmo popping more on the rosy base of In Stitches and the pink/rose showing more on the green of Uh Oh.
When I added a second coat of Pink Cosmo, over the colored bases, here's what it looked like:
And in the sun:
With all the duochromes that seem to be around now, it was probably inevitable that I found something close to Pink Cosmo in another recent collection. Swanky Silk is the one color I bought from China Glaze Bohemian because it seemed the most different from things already in my stash. Well, that's not so much true anymore.
In the bottles, they look pretty close. On the nails, you can see a difference. The China Glaze is thicker and more opaque; used two coats instead of the three for the Maybelline. I think it's the thickness of the formula that makes the brushstrokes more prominent in Swanky Silk compared to Pink Cosmo. Left to right below: Maybelline, China Glaze, Maybelline, China Glaze.
Same order, showing their golden side:
And in the sun, Maybelline on Top, China Glaze below:
If you have one of these already, you don't need the other. If you don't have either, I'd go with the Maybelline. Pink Cosmo looks more delicate and pretty to me, and its sheerness makes it more versatile for layering.