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BLUE STAIN
Blue stain (aka sap stain) is caused by a fungus that under certain conditions will spread into wood once it is removed from the stump. The fungus is frequently, although not necessarily, deposited on the tree by insects. The pine beetle, for example, frequently deposits the fungus on the tree just inside the bark. The beetle goes no further but the fungus can penetrate all of the sapwood. Since the fungus eats nutrients found primarily in the sap, it usually only occurs in the sapwood and not the heartwood. Once present, it cannot be removed. It does not occur in live trees because live sapwood does not contain enough oxygen to sustain the fungus. It is common in pine and maple but also occurs in many other woods such as anigre, prima vera, and aromatic red cedar (Eastern red cedar). The color is usually blue but may also be gray and or even dark gray verging on black. The color is the fungus itself rather than a chemically induced change in the color of the sapwood. There are extensive articles on the Internet discussing it and how to avoid it and even how to reduce its effect (but once it's there, you can't get rid of it totally --- you need to avoid it during drying). It does not normally start to affect logs for many days, sometimes weeks or more, and of course, sometimes not at all, but it CAN start immediately after cutting and have a pronounced affect within just a few days.
Examples:
Southern yellow pine log end with an excellent example of blue stain; enlargement present
red aromatic cedar with blue stain in the sapwood
anigre sapwood plank with blue stain
prima vera plank with heavy blue stain
narra plank with blue stain
padauk with blue stained sapwood
spalted sweet bay magnolia with blue stain
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slash pine with blue stain
ponderosa pine with very heavy blue stain
sycamore with blue stain