For mine, I used all Fair Maiden Polishes. The colors are Ooh La La (orange), Daredevil (red), Look on the Bright Side (yellow), Aim to Misbehave (green), Let's Get Physical (blue), Don't Be Shy (light warm-toned purple), Reach for the Sky (lavender), Tickle Me Pink (uhhhhh pink), and Glory of the Galaxy (glittery topper). You can use any polishes that are close to each other on the color wheel and get the same effect!
I used a makeup sponge and starting with the thumb, painted a stripe of red and a stripe of pink right next to each other on the sponge. I stippled these on the nail vertically, slightly moving the sponge each time so the colors blend to give a nice gradient. I went over each nail 3 times to get a fully opaque color. On a clean area of the sponge, I painted the next two colors for the pointer finger (yellow and green) and repeated this process. On the middle finger, I used green and blue; ring finger is the lavender and reddish purple; and pinky is orange and yellow. I then added the glittery topper to add some sparkle!
Now comes the fun part--water marbling!! If you'd like to see a how-to, I have one on my YouTube channel: https://youtu.be/xXDSfWoxUqI For this one, I used Alpine Snow from OPI and Essie Good To Go top coat. I tried a different clear polish but it wasn't working out very well--it was drying way too fast before I could even get the design drawn in. So if that happens to you, just try a different polish!