If you cut an indigo milkcap (Lactarius indigo), the mushroom will ooze a deep-blue milk that turns green when exposed to air.
L. indigo is one of the most common fungi used in traditional Mexican cuisine. The blue color disappears with cooking and the fungus becomes gray.
Images: Viktor Mar, Alan Rockefeller/wikipedia and Cotnis/flickr
via BioInfo http://ift.tt/UEa4ju