Thanks for coming to Health Care Magic. During exercise, the oxygen requirement increases as it is needed to make energy. Oxygen is carried and transported via blood cells and when there is increased demand of oxygen to the tissues/organ, blood supply of that area increases and overall as well giving the pink-red hue. Externally, this is more visible in the areas with rich blood supply & where the skin is very thin, face is one such area. However, if the blood oxygen is insufficient, it gives the purple/blue hue. There can be several reasons of decreased oxygen like high altitude to abnormal hemoglobin, heart problems etc. Please request your husband to visit a general physician who will do physical examination, blood & cardiac tests to check and confirm the causes and will advice treatment based on test results. All the best !