When I first started rug hooking back in the '90s, I went back and forth between fine hooking and primitive hooking. At the time, I was fascinated with shading flowers, and managed to hook a few 3- and 4-cut rugs. In my quest to find the perfect shading technique (!), I was lucky enough to get a copy of Mildred Sprouts "Design-A-Patts" book. I believe it dates to 1954.
"Design-A-Patts" is a manual for shading both flowers and fruits. Each plant has a picture with shading instructions and some of the patterns even having suggested formulas you can try. Here is a sample of shading techniques for an apple, banana, and cherry. The detail may be a little tough to see, but I think you'll get the idea. The following photo is a closeup of calla lilies that I hooked using help from Mildred's book. Had a lot of fun hooking this rug.
This book is still available. Try googling Mildred Spouts. If you have photos of shaded rugs, I'd love to see them and will post them on this blog.