Hue/Saturation <Ctrl+U>

You can adjust clarity and brightness of the photo.

Steps

Click Color > Hue/Saturation.
In the Hue/Saturation dialog box, enter each value or adjust the slider bars on Hue, Saturation, and Lightness under Color Adjustment.
Click OK.

You can select the desired channel from the list.

Hue: Adjust hue that is a value corresponding to a segment in the circularly displayed spectrum of visible light. The red color with the longest wavelength is the reference (0). The colors are in the order of the rainbow – Red, Orange, Yellow, Green, Blue, Violet and Purple.
Saturation: Adjust the clarity of a photo. 100 means that it has the most clear color and –100 is the zero clarity level, or gray color.
Lightness: Adjust the brightness of a photo. 100 represents the white color and –100 the black color.

You can turn a color photo into a single-colored photo. You can adjust the photo color by using Hue.