Larry -
Thank you for taking the additional photographs, they are at the perfect angle and very good quality. The only thing I forgot to tell you was to have an artificial light shine on the backing so as to be able to clearly see the detail of the texture and color of the backing.
The backing looks like rawhide from what I can see. Sort of looks like the surface of the back is very irregular and the rawhide is formed into the lows and over the highs of the back. That is typical of Grumley's rawhide backing on osage bows with some character on the back.
The color of some of his rawhide backed bows is almost translucent, others are almost a creamy yellow, and some like yours with light and dark. Clarified calfskin vs rawhide from various animals may be the explanation for some of this color variation.
It is wonderful to see the many variations in features of Grumley bows.
Nels was, and still is, truly the Michelangelo of bowyers for all time.