Why does the foot on my weak leg turn red and purple?

Here is My Question:
I was diagnosed with MS in 2013. I have lesions in all three areas (brain, cervical and thoracic spine). Current deficits include parathesia's, general fatigue and right leg weakness. I have a slight foot drop and limp. I am still able to move all my toes and foot and walk without assistance but my question is why does the foot on my weak leg get red when I am hot and purple when I am cold? There is also slight (non pitting) swelling when I have been on my feet for prolonged periods. I move my foot and leg so it is hard to believe this is some type of venous stasis. The toes on my weak foot are always slightly more pink or purple than those on my unaffected foot. Heat and cold make it much more noticeable. 

Answer:
A potential explanation aside from reduced return of blood from the leg to the heart due to your right leg weakness, would include an autonomic nervous system influence on the leg.  The autonomic nervous system helps regulate blood vessels in our body (ie, vasomotor stability or instability).  Normally, when it is hot out, your autonomic nervous system will prompt dilation of some blood vessels in the skin as well as stimulate sweat glands to help cool down the body.  Spinal cord lesions from multiple sclerosis can affect the autonomic nervous system (particularly if found near the center of the spinal cord), and therefore can alter normal autonomic nervous system function.  Your neurologist can weight in on this as a potential explanation for your symptoms.

A. Scott Nielsen MD MMSc
Neurologist and MS Specialist at Kaiser Permanente