So I woke up early this morning and sat in bed with a glass of mango iced tea, watching Saved By The Bell and then Zoolander and doing nail polish comparisons. It's nice to be a lady of leisure. :)
Anyway, there are colors in the OPI Shrek minis and in the Essie Resort Collection minis that reminded me a lot of other colors I already had, so I decided to do some comparisons. Unfortunately, it's super cloudy today, but I think I got some decent pictures.
First up, the greens... well, blue-greens. Turquoises, if you will. Pardon the bottle shots, they were all taken on my bed. :)

From left to right: Essie Turquoise & Caicos, China Glaze For Audrey, Orly Gumdrop, Revlon Minted, Essie Mint Candy Apple
The polishes are on my fingers in the same order, from thumb to pinky.

The greenest ones are Turquoise & Caicos and Minted.
I still say Gumdrop and For Audrey are dupes, or at least near dupes. For Audrey may be a TINY bit bluer.
Turquoise & Caicos is actually a jelly. I thought it was a creme til I put it on. Nope, it's a jelly. It's also three coats. Minted is also three coats.
Gumdrop was opaque in one coat.
The rest of the colors are all two coats.
Now on to the blues!

From left to right: Orly Snowcone, Essie Lapis of Luxury, L'Oreal High Tide, Finger Paints Blissfully Blue, OPI What's With the Cattitude.
The polishes are in the same order on my fingers, from thumb to pinky.

Snowcone was opaque in one coat.
Lapis of Luxury is another jelly, another three-coater, and I think it may be a jelly dupe for Snowcone, which is a creme.
High Tide is completely different from the rest of them.
Blissfully Blue and What's With the Cattitude are similar, but not dupes. Blissfully Blue is way more stark, while WWTC is a deeper blue. Blissfully Blue was opaque in two coats, while WWTC took three coats.
Here's Snowcone on my thumb and Lapis of Luxury on my pointer. They are SUPER close.

And now for the purples!

From left to right: Essie Lilacism, China Glaze Light as Air, OPI Rumple's Wiggin.
On my hand, they are in this order:
Pointer - Rumple's Wiggin
Middle - Light as Air
Ring - Lilacism
Pinky - Rumple's Wiggin

Light as Air was opaque in one coat.
Lilacism took three coats. Rumple's Wiggin took two coats.
Light as Air is considerably lighter and grayer than the other two. To my eye, Lilacism and Rumple's Wiggin are absolutely dupes. There may be a tiny difference between the two, but you'd have to really be looking for it to see it.
So there! I hope this is informative and helpful. Now back to Zoolander. :)