To do this mani I started with two coats of Savvy French White White with a coat of Seche Vite on top, below.
I have done a blue gradient mani once before using a makeup sponge, here. I have read that using a sea sponge can offer a better gradient effect so I picked up a faux sea sponge from the grocery store and cut pieces off of it to use for this mani. Below is a picture of what I used in case you aren't familiar with what I am talking about.
Then I used five different greens to create this effect in this order, China Glaze Into The Lime Light, China Glaze Gaga for Green, Orly Lucky Duck, OPI Don't Mess With OPI, and Ulta Envy.
I took pictures after putting on each of the colors, but there was green polish all over my skin... it wasn't very attractive so I decided not to add them to this post, lol. :) I covered the entire nail with the first and lightest color, and put less and less of each of the following colors as I went up the nail. Then when I was done I put a coat of Seche Vite on top.