colour for U.S. squadron codes

On OD B-17s, different bomb groups used different color codes. Some used gray, some used yellow, and some used white. 

Looking at 1943 color photos of different squadrons in the same group they had white fuselage codes and yellow individual letter on the tail.

Here is a link to a good page on the Bomb Group with lots of photos. Mostly b&w, but some color as well.

http://www.americanairmuseum.com/unit/324

That's great chaps. Thanks very much