For this gradient, I used a base of Sally Hansen Xtreme Wear Mint Sorbet. It's a little bluer in real life than it looks in these photos. Then I put a little pool of OPI Mod About You onto a piece of paper, dipped a makeup sponge into it, and applied it to my nail, starting at the tip. I use wedge sponges (you can find a pack for a couple dollars at any drugstore), and one sponge can last forever if you just tear off the bits that have dried polish on them!
It will probably take a few sponged-on coats to get the desired effect. Just remember to always start at the free edge (tip) of your nail, so that is where the color is most concentrated, and work your way towards the cuticle.
See? Totally easy-peasy, and it's great if you're indecisive like me and can't pick just one color to wear. It's the best of both worlds! (Is that Hannah Montana stuck in your head now? Yes? Thought so. Sorry.)
Gradients also look awesome when you use glitter polish, and it's a great way to ease yourself into wearing glitter if you think a full glitter mani is too much. Also, glitter gradients are even easier than this because you can just use the polish brush, like I did in my Hunger Games manicure!
PS--holy cow, my nails are long in this. Never again. I don't get it how girls can function with mile-long acrylics. Do you like, not need to type or text or tie your shoes or do dishes or...?