Color Constancy


This activity demonstrates color constancy, or the tendency for the colors of objects to appear relatively unchanged despite substantial changes in lighting conditions. In this case, there are 18 color swatches forming a simple visual scene. You will apply different lighting filters to that scene and see how your perception of color changes.


Choose “Blue Lighting” to see how the swatches look under blue light. You should notice that the color swatches don’t appear to change color much.

Now choose “Blue Rectangles” to see how the swatches look with the same blue light, but localized just to cover the swatches themselves. In this case, the swatches should appear to change color! For instance, the yellow patches in the first and second row should continue to look yellow when the blue lighting covers the entire area but should appear rather greenish when the blue rectangles are switched on. The gray patches in the bottom row should continue to look gray when the blue lighting is switched on but should appear to bluish gray when the blue rectangles are turned on.

Try the same procedure with the yellow, green, and red lighting to convince yourself this is not some artifact of blue light. Why do the swatches seem to stay the same color when the lighting changes are spread over the entire area but not when the lighting changes are confined to the color swatches themselves?

Note: To see the original color of a swatch while a light is “on,” simply click on the swatch and drag the overlaying rectangle off of the swatch. (Releasing the rectangle will snap it back to cover the swatch.)

Once you are ready, click this link for an explanation.

What’s Going On Here?

Human color perception is pretty robust to changes in lighting – this is the phenomenon of color constancy. When perceiving the color of a surface, the visual system discounts the illuminant. That is, it determines what variations in the color of a surface are due to the lighting source and subtracts that color away from the object to get a more accurate perception of what color the surface really is, not how it appears.

When the color rectangles are overlaid exactly on top of the color swatches, there is no evidence that this is a change of illumination because the lighting doesn’t also cover the regions in between the color swatches. So your visual system doesn’t know that this is a trick of lighting and assumes that the change in the color appearance of the swatches is a genuine change to their color, not an accident of lighting. Therefore, your visual system does not discount the illuminant, causing the color swatches to appear to change colors.

Overall, human color constancy is not perfect, but it does a good job of allowing you to figure out the color of an object in the world. You are not distracted by the local color on the retina because the system discounts the illuminant…even if it does not totally eliminate it.

Back to the introduction.