The Color Tools Color Tools.

Colorize

The Colorize tool limits the color range to a single color (scaled)
The original image.The Hue bar sets the color.  It is setup according to the color spectrum, beginning and ending in red.

The Saturation bar determines how much color is added.  If the saturation is "0" the picture will appear gray.

Blue.

Orange.

Gray.

RGB Color Shift

The RGB Color Shift tool adds red, green, or blue to an image.
The original image.

Red.

Aqua.

The other color tools are fairly self-explanatory.  Experiment and see all the powerful options available.

Brightness/Contrast
Auto Adjust Contrast
Gamma
Grayscale
Negative
Mono