Why is it when it it’s cold the body tends to turn dark and slightly hard?

Question: Why is it when it it's cold the body tends to turn dark and slightly hard?

Asked by 256bmay33 to Ann, David, Doris, Grace, Jonathan, Peter on 2 Jun 2019.
- Grace Kago answered on 2 Jun 2019:
  
  I think its because sometimes when we are cold, the body will make our muscles constrict so that it can squash the blood vessels that go to our fingers/toes to allow for more blood to flow to the main core organs to keep them warm. When the muscles constrict, they’re stiffer so then maybe that’s what feels “hard”? I’m not sure about the part about the body turning dark.. maybe my colleagues know that one!

Question: Why is it when it it's cold the body tends to turn dark and slightly hard?