cyanosis
Cyanosis is the change of body tissue color to a bluish-purple hue as a result of having decreased amounts of oxygen bound to the hemoglobin in the red blood cells of the capillary bed. Body tissues that reflect cyanosis are usually in locations where the skin is thinner, including the mucous membranes, lips, nail beds, and ear lobes. Cyanosis can also be a sign of necrosis.
Cyanosis - From Wikipedia, the free encyclopedia
Cyanosis is most commonly seen in erotic heavy-peril scenarios, such as drowning or hardcore asphyxiation, to show the character is moments away from suffocating.