I did mine a bit differently, as I didn't want to paint white over the top of glitter and end up with it lumpy, and certainly didn't trust myself to do neat lines freehand. Instead, I started with a base of white (Barry M Cotton) and use curved tip guides to tape off the central section of the nails.
Then I painted a silver glitter over the curved central section. This is 2true Sequins Christy, which is a lovely dense one-coater but with small particles which won't overlap the tape too much.
I topcoated over the silver to make it smoother (Christy has a rough finish to it), and then used the Color Paints to paint my rainbow. I removed the tape, added more topcoat, and there you go.
It's not as fantastic as PiggieLuv's, but I'm pretty damn chuffed with this! The Color Paints look fab over glitter, and I love the contrast of white and the colours. I included this blurry photo because it shows how glossy and juicy these colours are!
What do you think?