Like the Automatic Color Balance command, the Grey World Color Balance command corrects image colors, but it uses a different mathematical algorithm.
The premise behind this command is that the average of all colors in the image should be neutral. Although this may be a reasonable approximation for some complex images, it isn't true for all images. (For example, an image dominated by a blue sky.) You should therefore use your own judgement to determine if this command is appropriate for your image.
By default the Grey World Color Balance command balances in way that causes neutral objects to have approximately equal red, green, and blue components. When viewed on a typical computer monitor, this corresponds to a color temperature of about 6500k. The Grey World command allows you to simulate other color temperatures relative to 6500k by adjusting the Illuminant Temperature control to higher values (to produce cooler neutrals with larger blue components and reduced red and green components) or lower values (to produce warmer neutrals with smaller blue components and increased red and green components).
When not to use Grey World color correction: This color correction may not work well for very simple scenes with few colors, images with a limited range of hues (such as mostly blues), or simple computer-generated graphics.
To correct colors using the Grey World dialog:
Choose Adjust
> Color Balance > Grey World Color Balance.
The right preview window shows the image colors automatically corrected
with the Grey World algorithm.
In the preview window, center an important part of the image (such as a face). Pan the image by clicking and dragging in the preview window; zoom in or out as necessary.
In the Illuminant Temperature group box, type a value or drag the slider to change the image’s illuminant temperature from warmer tones (oranges) to cooler tones (blues). The default setting is 6500K, which gives the effect of a photo taken in typical daylight. Photos taken indoors tend to look more orange, while photos taken in bright sunlight tend to look more blue. Adjust the value to achieve the desired effect or until the colors look the most natural.
Click OK.
Automatically Balancing Colors
Using Source and Target Colors to Correct Colors Manually