Is it normal to experience skin discoloration while wearing a cast?

I injured my foot on 5/25/09 during a car accident.  Initially, I was told that it was just a foot sprain, but after continuing to experience pain, I went to a podiatrist who ordered an MRI.   The MRI came back showing a fracture to my cuboid bone and possible trabecular fracture to my fourth metatarsal,  By the time the MRI came back it had already been almost 4 weeks since I had been hopping around on my foot.  It has now been a little over 2 weeks since I've been wearing a cast and 7 weeks since the accident.   I have a fiberglass cast and I notice that my injured foot is markedly darker than my other foot. I asked my podiatrist and he said that it was normal and that the color would come back.  I keep my foot elevated as much as possible, but I am concerned about the circulation to that foot as that could impede healing.  Is it the weight of the cast and the injury that is causing the problem or could there be something elso going on, especially since I am 7 weeks post-injury?  Also I am experiencing pain on the plantar surface of my foot.   'Before I put the cast on it only occured during the push off phase of my gait.   Could I have injured one of the ligament or tendons on the bottom of my foot or is the pain a part of the cuboid/4th metatarsal injury?  The MRI said that the flexor and extensor tendons as well as the lisfranc ligament appear to be intact, but I still have pain.  I would appreciate any advice you could give me.

[Yena H Do, DPM]

try to keep your walking to a minimum while you heal.  the discoloration is normal.  you had an injury to the foot and there was bone breakage, which involves bleeding, which seeps into the tissue.  it's like having a skin bruise.  
if you are experiencing pain, have the podiatrist apply more padding to the bottom of the foot b/f applying a new cast.