Blue snow....huh?

Blue snow is created by Eastern Cottontail rabbit (Sylvilagus floridanus), sometimes deer, that are feeding on particular types of plants.  Up here in NW Minnesota this particular plant is the European Buckthorn (Rhamnus cathartica).  As the Cottontail consumes the berries or bark of the Buckhorn there is a chemical reaction takes place when it's exposed to sunlight or oxygen due to oxidized phytochemicals...Urination in other words.

Reference:  

Minnesota DNR Invasive terrestrial plants > Buckthorn