On this video tutorial photographer Glyn Dewis shows a simple yet useful tip for working with a layer mask for fixing skin tone after some other color changes were done to the image in Photoshop.
Dewis starts to color retouch this image by adding 3 different LUTs (which are very similar to filters that already exist within Photoshop). He uses them one on top of another but with about 20% opacity or so.
These LUTs look nice on this retro outfit however they don’t look very good on the skin. You can of course add an adjustment layer and just paint with black but in this case you will get a very pink looking skin which does not seem natural. If you are thinking on just using your brush at say 50% you will discover that your strokes will make the adjustment layer uneven which again does not look very good.
Dewis solution is to add a layer mask and paint the face but open the properties of the layer mask and move the density to about 50% – this will give you a much more even reduction and the face looks much more natural.