Seeing in Colour We perceive a spectrum of colour because objects selectively absorb some wavelengths of light and reflect others. Colour perception corresponds to the relative activity of the three types of cones. Each type is most sensitive to a narrow range of wavelengths in the visible spectrum—short (bluish light), medium (greenish light), or long (reddish light). Rods, represented by the white curve, are most sensitive to the medium wavelengths of visible light but do not contribute to colour perception.