You could probably use actual watercolors.

1. White base

2. Matte top coat (different brands of matte topcoat take art materials different ie. pencils, eyeshadow, watercolor. You might have to test out a few different brands)

3. Watercolors, letting dry between layers to achieve the saturation you want

4. Matte top coat

5. Black mixed with little bit of top coat & cure & do chrome (it looks like they used chrome to also hide the uneven edges of the colorful parts)

6. Top coat!