This is a nice like purple/green duochrome neatly named Mash-Up. This is supposed to be inspired by the Glee character Will Schuester, who is the Glee Club teacher and tries to encourage the kids to make mash ups of songs. As a random bonus, here are two "mash up" songs not done by Glee, but by random YouTubers that I like.
And back to the nail polish.
I used a base coat of OPI Natural Nail, 2 coats of Mash-Up and a top coat of OPI Top Coat. Formula was a bit watery but okay. Depending on how the light hits you, you'll see green, grey, purple or even a silver shimmer.
Shade:
Overall, it's a bit of a weird color. I'm not sure that I'd buy it again, considering the price and it's more of a novelty thing. Many polish brands have their own type of swirly duochrome in this vein, so... ^_^
You can purchase Sephora by OPI in Sephora stores or online here for $9 a bottle. The actual Glee line can be found here