I spotted this cool set in TK Maxx, and you can still buy it on their website if you like the idea too.
You get five base colours, five empty bottles to make your colours, and a dropper to measure your paint. It's a lot messier than I expected, but it's fun.
I made a sunset orange shade first. It's quite patchy when I painted it on my nails, so it would take at least two coats.
What other colours should I make? Let me know on Twitter @rudedoodle