Final answer:
The blue appearance of the skin resulting from the presence of dark red deoxygenated hemoglobin is called cyanosis, which occurs due to low oxygen levels in the blood.
Step-by-step explanation:
The skin appearance that results from dark-red hemoglobin is commonly known as cyanosis. Cyanosis occurs when there is a sudden drop in oxygenation, affecting skin color and causing it to turn ashen or white at first. If oxygen levels remain low, the darker, deoxygenated form of hemoglobin, which is dark red in color, becomes more prominent, and the skin can appear blue. This can happen in medical conditions where oxygen supply is restricted, such as with asthma or during a heart attack.