I have seen this with our Amazons over the years. More commonly when the leg and claw are held-up into the feathers while the other is carrying the weight, if you will. When the leg that has been held near the body is set down, it appears lighter in color.
As you know, the big concern is whether there has been a loss of blood flow and that is a foundation for a fast trip to the CAV. At this point, watch for the next couple of hours (at most) and there should be a balance of color that should return. If not, be ready to be on your way.
If your Parrot has been holding one leg in the feathers, it will naturally be warmer than the one that is being stood upon. This makes checking for a temperature difference near impossible. Now, if none of this is true, i.e., both legs are being used to keep him up right, check if there is a temperature difference. If you note a difference, call the CAV for a phone evaluation.