Standard model-making paints (e.g. Revell) work great with PA12 (SLS) and Stereolithography materials. Both acrylic and water-based paints work as well, but several layers may be needed. 

Since PA12 has a porous structure, the result of applying paint directly will not look good. Therefore, it’s better to first use a primer that puts a preparatory coating on your model before painting. Some clients thoroughly clean their model with water first and let it dry for several days before starting to paint. 

Stereolithography materials will be easier to paint. Also, start with a primer first to smoothen the surface of your model. This way, the visible level structure of the 3D print process decreases. 

Please do not use any harsh paints because some chemicals may degrade your models or react with the 3D printing materials. When painting, wear a mask, use caution and ensure plenty of ventilation.