How to make tinted nail polish from clear and mascara or other powdered pigments.  Works with glitter too.

DIY: How to Make Nail Polish with Eyeshadows & Pigments

From Makeup Geek: Create your own nail polish using pigment or eyeshadow, clear top coat, and a plastic baggie. This would be a good way to get use out of some old eyeshadow that you know you'll never use. I have a few of those lying around!