The present disclosure provides a pixel unit including a plurality of sub-pixels of different colors. Each sub-pixel includes a first transflective layer, a wavelength selective cavity, and a second transflective layer disposed successively along an incident light direction. A height of the wavelength selective cavity of each sub-pixel in the incident light direction is designed so as to select light having a wavelength corresponding to a color of the sub-pixel from light which is incident through the first transflective layer and reflected between the first transflective layer and the second transflective layer, and selected light exits through the second transflective layer. The present disclosure further provides a display substrate and a display panel.