1. First open up a picture you want to apply a color masking to.
2. Now create an adjustement layer by clicking on this icon:
nd then select Hue/Saturation.
se these following settings:
Hue: 0
Saturation: -100
Lightness: 0
Now you should have a layer like this one:
3. Now select the brush,and set the foreground color to black or any dark color, and then colorize the Hue/Saturation layer you just made.
If you want to earase what you just colorized, change the foreground color to white, and with the brush paint where you want to erase.
More Tutorials: 
