An electronic device may have a display with a cover layer. An ambient light sensor may be aligned with an ambient light sensor window formed from an opening in a masking layer on the cover layer in an inactive portion of the display. To help mask the ambient light sensor window from view, the ambient light sensor window may be provided with a black coating that matches the appearance of surrounding masking layer material while allowing light to reach the ambient light sensor. The black coating may be formed from a black physical vapor deposition thin-film inorganic layer with a high index of refraction. An antireflection layer formed from a stack of dielectric layers may be interposed between the black thin-film inorganic layer and the display cover layer.