Carboxyhemoglobin (carboxyhaemoglobin), the complex formed when carbon monoxide reacts with hemoglobin (haemoglobin) is bright cherry-red in colour (as opposed to deoxygenated blood, which is bluish and oxygenated blood which is red).
Treatment is with supplemental oxygen. Severe carbon monoxide poisoning may require hyperbaric oxygen therapy, where the poor patient has to sit in a pressurised chamber (essentially the same kind of chamber used for curing divers of 'the bends') until the carbon monoxide in his system has dropped down to an acceptable level.