Now select the Mask of the Adjustment layer.
Select a brush of suiting size for your subject.
(Having a bigger brush to paint the center of the surface then selecting a smaller when getting closer to the edges is usually a good idea.)
Finally paint the areas where you would like the color to be visible with a black brush. If you paint something you don't want to be there then simply paint it away with a white brush.
That's it. This is something worth playing around with, trying things like Gaussian blur, Crystallize etc. In some photos setting the Adjustment layer opacity to about 70% can also create an interesting effect