Pallor mortis (Latin: pallor "paleness", mortis "of death") is a post mortem paleness which happens in those with light/white skin almost immediately (in the 15–25 minutes after the death) because of a lack of capillary circulation throughout the body. The blood sinks down into the lower parts (due to gravity) of the body creating livor mortis.
Paleness develops so rapidly after death that it has little to no use in determining the time of death, aside from saying that it either happened less than 30 minutes ago or more, which could help if the body was found very quickly after death.
Also, a living person can look death-pale. This can happen when the circumstances make the blood escape from the surface of the skin, as in deep shock. Also heart failure (Insufficientia cordis) can make the face look gray; the person then also has blue lips.