This tool lets you adjust the saturation of the pixels you paint on.
The same settings are available as for the brush tool (see Brushes) except the following settings are also available:
Here, choose whether the tool should saturate or desaturate the pixels you paint on.
This parameter defines the strength of the effect. The more you paint over the same pixels, the more saturated or desaturated they become (provided you keep releasing the mouse button between brushstrokes).