I've seen this a lot! And of course, really wanted to try it out myself. Yall know how much I love creating stuff and DIY projects :P
I didn't even took pictures while doing this, for a step-by-step pictures tutorial, because I really wasn't sure how good or bad will it turn out. But not that it turned out well, it turned out b-e-a-u-t-i-f-u-l! :D The nail polish looks as amazing as (if not prettier than) the eyeshadow!
So I used the MAC miniralized eyeshadow in young punk, and just a clear nail polish from the drugstore. As I wasn't sure how it'll turn out because it was the first time I've ever tried this, I didn't even mixed the polish with the eyeshadow in a nail polish bottle or something. Instead, I crumbled a little bit of the eyeshadow to an bottle lid, and poured some of the clear nail polish into it as well. Then I mixed them up together very well until I got an even texture. Then I just painted my nails with it using the brush from the clear nail polish. I only had to use 2 coats to get this really opaque result! Finally, I've used a top coat to finish.
Now I want to try this more and more! And if I have an eyeshadow that I really like and wish I had the same color nail polish or could use it on my nails, or if I just want to match my eyeshadow with my nails - problem solved!! :)