Lactarius indigo, also known as the blue milk mushroom, ranges from light blue to dark blue. They can be poisonous. They are very pretty if you see pictures.
To create those lovely fungi on my accent nail, I started with two coats of Pure Ice Wild Thing. Then I sponged on Ulta The Jungle Look and Sinful Colors Black on Black. Finally I added my blue mushroom with BM-302 and Sally Hansen Pacific Blue. The rest of my nails are two coats of Pacific Blue.
BM stamping plates are part of a 25 piece set (the 2012 one) that retails for $22 on Bundle Monster or their Amazon store. Pure Ice retails for $2 at Walmart and Bari Cosmetics. Ulta Nail Lacquer retails for $6 at Ulta. Sinful Colors retail for $2 at Walgreens (online/in store) and Target (in store). They're also available for $2.50 at Cherry Culture. Sally Hansen Xtreme Wear retails for $2-3 at Walgreens, Walmart, Riteaid, Target, and Ulta.