*EDIT - Here is a video on how to do this technique. I don't have a way to record a video right now so use these to guide you on how to do this: Professional DQ does Unicorn Drool.*
So I saw a video posted where a gal actually used watercolor pots to create a spotted look so I looked up the watercolors she used and they were a UK brand. On a hunch that watercolor is probably watercolor (pretty good deduction skills right!) I bought the cheapie 3.99 Pearlescent watercolor set from the Fred Meyer art section. I grabbed a regular brush I had laying around, got it a touch wet and went for it.
The colors were inspired by my accessories. I've been really getting into rings and bracelets lately:
I Heart Pretty Polish. I just love her pose so much <3
Basically grab a set and go for it - it's cheap and gives splendid results that you'll love showing off. I know I did ;)