A mother brings her newborn to the hospital concerned about a blue patch on the buttocks. The newborn is of mixed race and was delivered normally. What is the most appropriate management?

The key is A. Reassurance. [The diagnosis is mongolian blue or spot. Mongolian spot refers to a macular blue-gray pigmentation usually on the sacral area of healthy infants. Mongolian spot is usually present at birth or appears within the first weeks of life. Mongolian spot typically disappears spontaneously within 4 years but can persist for life. It is a benign condition requiring no intervention].