I've seen a few manis like this over the last few months, where watercolour polishes are used over glitters. I did this mani more than a month ago, so now I don't even remember what glitter I used as my base, but it was a silver glitter than had a mix of small and larger glitters as well as holo glitters.
For the watercolour markings I used all four of the Ulta3 watercolour polishes. I applied them using a dotting tool in various patterns. I did two layers to build up the colour, as these Ulta3 watercolours are not as pigmented as the OPI ones.
I also ensured I used a PVA peel off base coat on this one because the glitter was applied very dense and with the watercolours on top as well as a nice thick layer of Seche Vite, these nails were pretty much bullet proof.
This is such an easy design to create, you can be messy with the colours on top and it doesn't matter at all.