HSVBoost allows you to boost, reduce, or shift a surface color's hue, saturation, or value. More importantly, these color attributes can be modified based on the angle of the surface to the camera.
This is not an effect that is needed very often, but for some real-life surfaces it can be very appropriate. One of the best examples are tropical fish which have colorful skins that are covered by nearly-transparent scales. When you view the fish from the side, the brightly colored skins show through the outer scales and you see very colorful fish skin. However, if you view the fish at an angle, the outer translucent scales start adding a milky whiteness that robs the colors of their richness. The HSVBoost tool can emulate this effect by using a different boost of the surface color's saturation based on the angle of the surface to the camera.