Hatchlings use egg teeth to help break through the shell during hatching, but these structures could have an additional function of increasing nestlings' visibility. I investigated the size, color, and persistence of egg teeth in woodpeckers, which nest in dark cavities. Many species of woodpecker have two egg teeth, one each on the tip of the maxilla and of the mandible, which, together with the pale flanges, frame the open mouth when nestlings gape. A spectrometer confirmed that reflectance of Northern Flicker (Colaptes auratus) egg teeth is higher than that of the flanges across a wide range of wavelengths, reaching nearly 100% reflectance in the wavelengths most visible to woodpeckers. Reflectance of flanges peaked in the ultraviolet, which is less visible to woodpeckers. Therefore, parent woodpeckers can probably see egg teeth better than flanges. Within a brood, the brightness of egg teeth or flanges was not dependent on nestlings' size (hatching order), suggesting these structures are not cues of nestlings' quality. Flickers retained upper egg teeth until fledging, but the size of egg teeth did not increase after hatching. A review of the literature suggests some burrow-nesting seabirds also retain egg teeth for a long time, reinforcing the idea that egg-tooth reflectance may have evolved independently in several phylogenetic groups in which parents must find nestlings in the dark.