Fingernails appear to turn gray or blue after a person dies because the blood, full of oxygenated red blood cells, no longer flows underneath the nail bed. The natural color of the nail then shows. The nails do not actually change color, because like hair, the nails are not living tissue. During life, only the nail root contains living cells.
After a person dies, overall body changes include the drying out of body tissues containing water. As the skin dries out, the nails and hair can appear to grow longer as the skin shrinks and retracts. During life, certain diseases or medications can cause nails to appear to be blue or gray. When a person has pneumonia, or any illness or condition that causes difficulty breathing, lack of oxygen in the blood can turn the nail bed gray or blue, along with the lips. Raynaud's phenomenon refers to the severe restriction of blood flow to the extremities in response to cold or emotional stress, including the fingers, causing them to turn white, then blue. The fingers may be numb or tingle, then become bright red when blood flow returns. Blue or gray nail beds can be a sign of serious illness, and when combined with difficulty breathing, constitute a medical emergency.