For the Gradient map type, you can set or modify the following parameters in the Output rollout:
Invert: Inverts (reverses) the hues of the gradient, like a negative color photo.
RGB Level: Multiplies the RGB values of the gradient colors by the amount set by the spinner, which affects the saturation of the color. Eventually the gradient becomes fully saturated and self-illuminated. Lowering the value decreases the saturation and makes the gradient colors grayer.
RGB Offset: Adds to the RGB values of the gradient colors by the amount set by the spinner, which affects the tonal value of the colors. Eventually the gradient becomes white and self-illuminated. Lowering the value decreases the tonal value towards black.
Output Amount: Controls the amount of the gradient map being mixed into a Composite material.