The mathematical formulas of the projection light intensity of a 45?twisted nematio liquid crystal light valve (LCLV) are derived in detail, based on a simplified hydrid field effect mode. With the formulas, we have shown chromaticity diagrams of the pseudocolor under verious directions of LCLV. The chromaticity characteristics of this pseudo-coloring method is discussed, and the optimum rules of LCLV's directions are presented. Finally, the color adjustability and color confusion phenomenon in this pseude-color encoding technique are analysed.