The Sponge Brush
The Sponge Brush is pretty handy if you want to tone down the color or build it up in an area of your photo. If you want the green of a forest to be just a bit greener, or sky a bit bluer, this is the tool for that. Or if your model has poured on the spray tan, you can ton it down some with this brush.
Like everything else….try it and get to know how it works. It will take time and practice.