Dark circles under the eyes that are blue in color are caused by oxygenated blood pooling beneath the under-eye skin. Dark circles that are brown in color are caused by hyperpigmentation, which is caused by chronic eye-rubbing, sun exposure or genetics.
Blue under-eye circles are more noticeable in the morning because sleeping in a horizontal position causes fluids to accumulate beneath the skin under the eyes. The veins also expand to hold more blood. These dark circles are often treated using topical creams that contain stimulating ingredients that constrict blood vessels while temporarily increasing blood circulation. Brown under-eye circles are most often seen in those of Asian or African decent. They are often treated using serums or creams that contain skin brighteners to lighten the skin under the eyes.