USAAC Forest Green Uniform

I just finished reading, "On a Wing and a Prayer" by former B-17 navigator Harry H. Crosby. There's a B/W picture in it of the author wearing a so-called "Forest Green" uniform. Never having heard of this before, I was wondering if anyone had any information on it, e.g., what color was it actually, was it authorized for wear only in the ETO, was it only used temporarily, etc.

Thanks,

Tom