The GretagMacbeth ColorChecker White Balance card is a full size version of the white reference square used in the standard 24-patch ColorChecker. This white is scientifically engineered to provide a precise uniform surface that is spectrally neutral (reflects equal amounts of red, blue and green) in all types of light conditions. The photographer can now have confidence that the camera's raw image is as close to real life as possible.
ColorChecker White Balance gives photographers a way to adjust the digital camera's color sensitivity to exactly match the ambient lighting conditions, in effect, change what that the camera "sees." The perceived color of white often changes based on ambient conditions - outdoor it is perceived to be cooler, indoor it is perceived to be warmer and under fluorescent light it is perceived to be greener.