Green Color in Freshly Sawn Black Walnut

Freshly sawn Black Walnut sometimes shows a green tinge, which quickly fades. Here's more on Walnut's natural color behavior. October 14, 2008

I've just finished sawing my second "Oregon" black walnut and noticed a green color on fresh sawn boards. The first fresh cut log looked almost like a copper sulfate stain but disappeared after the surfaced dried for 24 hours. The second, stored in a barn for two or three years, showed a moss green color with yellowish streaks that faded within three hours. I've asked locally and it seems to be common. Does anybody know what the cause of the color is? Is it a bad thing?

Forum Responses
(Sawing and Drying Forum)
From Gene Wengert, forum technical advisor:
Green is the normal color and then it oxidizes to the dark color (similar reaction to an apple turning brown when left out in the air). In fact, fresh walnut furniture will darken with time.

From contributor A:
The log in the photo is an old walnut log. You can see in the middle where it is green it is still "wet" The outside had dried and turn brown. The silver dots are bullets. In fresh sawn green logs you will see an olive drab color and the sapwood will be white, then you will notice a purple to light blue tint as the logs starts to dry and oxidize. Dead stack it and heat it up to 200 degrees with steam and hold for about 72 hours and it will all turn a coco brown. Just sticker and air dry and it will have more color variation with the sapwood turning light gray to tan.