The Color Grade tab (pictured below) allows you to apply complex color correction to a loaded raster file. Color Grading is applied to RGB values after any Color Balance or Contrast Adjustment is applied. You can setup the input range for each color channel and what output range to map it to, as well as specify a saturation value.
Color Grading transforms the visible 8-bit RGB values to a new range based on the adjustments.
One example of the use of Color Grading might be with aerial imagery taken at different time periods. The example below shows two images taken during different aerial image surveys.
Using Color Grading the image on the right was adjusted to better match the colors on the left. Because the image on the right was lighter, by decreasing the input and output range for each color channel, the image will have less white tones.
In the example below the image on the left has a decreased saturation value of 0.6 to produce more muted tones that better match the image on the right.