Can nail polish be used on jewelry?
When considering the compatibilty of coating materials, the intended use (jewellery) is less important than the base material.  Nail polish/paint sticks well to some materials and not others. Without knowing what your "white" jewellery is made of, we can't tell you whether it wil stick well. 

It's not really designed to be permanent, so I would advise against it for pieces that are meant to last.  For temporary modifications it could be excellent, with caveats. Although it will chip fairly easily, there will be some bits left. Getting the last traces off is easy on metal/glass/stone materials (using acetone), but if there's any plastic or glue the acetone (nail polish remover) is likely to damage that.