A four-color transmissive display system incorporates a display having independently variable light sources for different colors, and a controller. The controller is configured to receive and process a three-color input image signal, and provide a four-color output image signal to the display. The controller incorporates units respectively configured to (1) calculate a blue reduction factor for each pixel, dependent on luminance differences between blue and other color components, (2) produce respective saturation adjustment factors for red, green, and blue, (3) apply the blue reduction factor to reduce blue luminance, and apply the saturation adjustment factors to reduce saturation of other colors, (4) produce the output image signal. An optional sensor is operable to provide a control signal to the controller, whereby display power can be reduced. An optional estimating unit is configured to estimate current required to display the input image signal, for adjustment of the output image signal.