“The Gray Card is a process control benchmark for color management. Without one our camera, monitor and printer are only as good as our eye’s ability to discern color, and our eyes are easily fooled. Absent any external reference our eyes will accept a wide range of variation in color as being normal. That’s due in part because in real life we experience things under a wide range of light conditions.”
“For lack of a better tool the arbiter of when color is neutral for most photographers is the toolbar eyedropper tool in Photoshop. It should be set to 5 x 5 sample size for measurements which will average out any pixel-to-pixel variation. When a photo contains an image of a gray card which is known to be neutral, an eye dropper reading on the card will reveal from the RGB values how accurately the color balance in the camera was.”
