Hi Margo,
There was a little method to my "random" pinwheel layout also. I started by sorting all of my pinwheel half square triangles (HSTs) in stacks by fabric (or color for a few unique scraps used). Next, I divided each stack into four stacks--one for each side of the border. That way, I would have the same number of HSTs for each fabric/color on each of the four sides of the border--evenly distributing the colors and fabrics. Then, I sorted all of the HSTs for each border side to create unique pinwheels without duplicating the same fabric in any pinwheel. Lastly, I laid out the pinwheels for each border side such that touching HSTs did not have any of the same fabrics, or at least the same fabrics were not touching in adjacent pinwheels. Since I had a lot more pink fabrics than yellows or greens, I made a couple of all pink pinwheels and placed them in opposite diagonal border corners. For balance, I placed an all green pinwheel and an all yellow pinwheel in the other two border corners. I'm pleased with the result.
Unfortunately, I cannot post a photo until I get my PC fixed. I'm currently using a borrowed PC which has no photo handling software.