I had a fiberglass cast on my leg for 3 weeks in july 2013. i have a lot of hyperpigmented areas still on my leg. is it due to the cast or crps?

Hemosiderosis: You are describing hemosiderosis, which means iron stained deep pigmented dermis. Deeply bruised or contused skin tissues often will end up permanently stained by the iron products broken down from the blood in the bruise. Likely your broken or injured leg was deeply bruised or contused at the time of injury, and the residual staining is from the injury. It will fade over time.