Canon 10D User Guide (en)

You can adjust white balance using a selected part of an image as the 
standard for white to make the image appear natural. Using click white 
balance is effective when using it in parts of an image where white color 
tone has changed under the influence of a light source.
Click the [
] button.
Adjusting Color Tone Using Click White Balance
Click on a point that is to be the standard for white.
The color of the image is adjusted with the point you selected as 
the standard for white.
If you click on another point in the image, the white balance is 
adjusted again.
To finish click white balance, right-click with the mouse or click 
the [
] button again.
The coordinates of the cursor position and 
the RGB values (8-bit conversion)
When there are no white areas in your image, you can adjust the white 
balance by clicking on a neutral grey point of the image in step 2. This 
has the same adjustment result as selecting a white point.
When there are no white areas in your image
The image is adjusted based on the average value of 1 × 1 pixel 
range from the clicked point.
The histogram display changes according to adjustment. You can 
also fix the histogram display to the display before any