Ключевые слова: acquired, blue, bluish, cardiac, central, changes, chronic, color, congenital, covid, covid 19, cyan, cyanosis, cyanotic, dark, discoloration, discolored, discolouration, discoloured, disease, disorder, dorsal, finger, fingers, hand, hands, healthy, heart, hypoxemia, hypoxia, ill, illness, induced, lung, pale, pallor, patient, problem, purple, respiratory, skin, smoker, smoking, stain, surface, unhealthy,