The following quote is taken from Alan Gunn, Essential Forensic Biology, 2nd edition, Wiley-Blackwell, New York 2009, pp. 20-22 (italics mine):
«Sometimes the cause of death may result in striking changes to normal skin coloration. For example, deaths from carbon monoxide poisoning often result in a cherry red / pink coloration to the skin, lips and internal body organs (…) although if the body is not discovered until several hours after death the coloration may not be immediately apparent owing to the settling of the blood to the dependent regions [livor mortis].
Carbon monoxide gas forms during the combustion of many substances and poisoning is a common feature of accidental deaths in which people are exposed to fumes from a faulty gas boiler or during fires and suicides in which the victim breaths in vehicle exhaust fumes. (…) Carbon monoxide has much greater affinity than oxygen for the haeme molecule of haemoglobin and therefore, even at very low atmospheric concentrations it will rapidly replace it and thereby reduce the oxygen carrying capacity of the blood. When carbon monoxide binds with haemoglobin in the blood or myoglobin in the muscles it forms carboxyhaemoglobin and carboxymyoglobin respectively and they are responsible for the pink coloration
There are cases in which carbon monoxide poisoning does not result in the formation of a cherry pink coloration (Carson & Esslinger, 2001) and it can be difficult to spot when the victim is dark skinned – though it may be apparent in the lighter regions such as the palms of the hands or inside the lips or the tongue. There are big difference in susceptibility to carbon monoxide poisoning and this is at least partly a consequence of age, size and general health. For example, children tend to be more susceptible owing to their higher respiration rate».
In my essay “Skin discoloration caused by carbon monoxide poisoning –
Reality vs. Holocaust eye-witness testimony” I have found, based on medical-forensic reports relating to a total of more than 600 cases of carbon monoxide poisoning, that “a clear cherry-pink coloring of livor mortis” is present in 95-98% of all fatal cases of CO poisoning. That the Aktion Reinhardt key witnesses Rudolf Reder, Jankiel Wiernik and Eliahu Rosenberg describes the supposed victims of carbon monoxide gassings – victims whose bodies they allegedly dragged from overcrowded gas chambers to mass graves, a work which must have taken several hours – as being without discoloration, yellow, or gray-white respectively, is enough to draw the veracity of those eyewitnesses into question.