An electronic device may be provided with light sensors. The electronic device may have an electronic device housing in which a display is mounted. The display may have a transparent layer such as a transparent display cover layer, a thin-film transistor layer, or a color filter layer. An opaque masking layer such as a layer of black ink may be used to cover an inner surface of the transparent layer in an inactive area of the display. Sensor window openings may be formed in the black ink layer. A layer of ink may be formed in each sensor window opening. Each layer of ink may have a diffuse reflectivity that is matched to that of the black ink. A diffuser layer such as a polymer coating layer with light-scattering particles may be coated on the inner surface of the layer of ink in a sensor window opening.