System Three® makes a number of self-leveling epoxy coatings which are extremely durable when cured, and don't need any additional protection used indoors. When used outdoors though, they will weather in the sun and should be coated with a UV-inhibiting coating like our Spar Varnish or WR-LPU.
Decorative paints are easily applied over or under these coatings. If applied first, or underneath, they will need to be thoroughly dried or cured, and then sanded with no finer than 120-grit sandpaper to ensure good adhesion of the self-leveling epoxy.
To apply decorative paint or artist colors over the epoxy, simply allow the resin to cure, then prepare the epoxy surface according to the paint manufacturer's directions.
As always, make sure to run a small test with the desired material prior to applying it to your entire project.