A reflective display's color gamut depends on both the intrinsic red, green, and blue primaries of the display and the illumination spectrum. Cholesteric liquid crystal layers are utilized in reflective displays to reflect light of a particular wavelength and transmit all other light wavelengths.
A cholesteric liquid crystal consists of a nematic liquid crystal and a chiral additive blended together to spontaneously form a helical structure with a defined pitch. This pitch determines the wavelength of light reflected by and hence the perceived color of the material. A pixel in a cholesteric liquid crystal display can be switched between its planar reflective state and its semi-transparent focal conic state, by application of an appropriate drive scheme. In its reflective state, the observed color of the device is a combination of the cholesteric reflection and the background color.
A full color cholesteric liquid crystal display can be made by stacking a set of red, green, and blue reflecting liquid crystal panels on top of each other. A typical display configuration with diffuse illumination at all angles provides an observed color that depends, in part, on the observed viewing angle. The observed color shifts to shorter wavelengths at more oblique angles from normal or on-axis. This effect is undesirable in a display as it leads to diminished color saturation in the observed image.