This isn't much of a gradient really since the colours don't "blend" into each other. I chose to sponge on the rainbow because I didn't want to mess around with tape and getting straight lines (read: I'm lazy).
What I used:
L to R: OPI What's With the Cattitude, American Apparel L'Esprit, China Glaze Something Sweet, TBN Anna Loves It!, China Glaze Lemon Fizz and China Glaze Re-Fresh Mint. (They look so pretty lined up together!)
All sponged over a coat of Revlon Powder Puff with stars from plate M17.
I'm loving the way it turned out but I kind of wish I'd done the rainbow on the diagonal - I think it would've looked better that way. Still happy though! It's so cheerful :)