A paper by Mark Changizi in Elsevier's journal Medical Hypotheses cleverly suggests that hospitals issue gowns matched to skin-tone for new patients, so that it's easy to tell if skin-tone has shifted (an urgent warning sign of many urgent health conditions):
One potential solution, Changizi said, is for hospitals to outfit patients with gowns and sheets that are nude-colored and closely match their skin tone. Another solution is to develop adhesive tabs in a large palette of skin-toned colors. Physicians could then choose the tabs that most closely resemble the patient's skin tone, and place the tabs at several places on the skin of the patient. Both techniques should afford doctors and clinicians an easy and effective tool to record the skin tone of a patient, and see if it deviates – even very slightly – from its "baseline" color over time.
"If a patient's skin color shifts a small amount, the change will often be imperceptible to doctors and nurses," Changizi said. "If that patient is wearing a skin-colored gown or adhesive tab, however, and their skin uniformly changes slightly more blue, the initially 'invisible' gown or tab will appear bright and yellow to the observer."