Dynamic ornamental signals that vary over minutes, hours or weeks can yield continuous information on individual condition (e.g., energy reserves or immune status), and may therefore be under strong social and/or sexual selection. In vertebrates, the coloration of the integument is often viewed as a dynamic ornament, which in birds can be apparent in the beak. King penguins (Aptenodytes patagonicus) are monomorphic seabirds that possess conspicuous yellow–orange (YO) and ultraviolet (UV) beak spots that are used by both males and females in mate choice. We studied the dynamicity of beak spot sexual traits, and to what extent they reflected changes in individual condition in fasting king penguins and in penguins treated with an anti-parasitic drug. We also describe the maturation of this colorful ornament during the yearly catastrophic moult. On a time-scale of days to weeks, beak spot coloration changed in response to fasting and experimental changes in parasite load. Beak spot UV brightness decreased over a 10-day fast in breeding birds. For birds caught during courtship and held in captivity YO chroma decreased after a 24-day fast. Birds that were treated with an anti-parasitic solution showed an increase in UV coloration after parasite removal. Altogether, our results show that beak spot coloration is a dynamic ornament that reflects multiple dimensions of changes in individual condition in breeding-fasting penguins.