Nursery idea--dark gray walls for a boy??

Sa
We just found out recently we are having a boy..so bye bye to all the pretty pink and purple nursery ideas I've collected on pintrest..for now anyway :) 
I'm not a crazy big fan of pastels and traditional baby blue boy nurseries so I went searching for something a little more unique. 
I've fallen in love w the idea of a gray and rainbow boys room. What do you ladies think? Is it too out there and dark? 
Edit: this isn't my house, btw, but something I gleefully ripped off Pinterest for my idea board :)