I am attempting to use a layer mask in PS CS and cannot get it to work. I have reviewed two tutorials and am fairly certain I am doing it correctly. When I apply something [desaturation for example] to the adjustment layer and then click on the layer mask and select either white or black and paint it does nothing. It does not show anything being done in the layer mask thumbnail as illustrated in both tutorials. I have tried to look at the mask properties to see if something is set incorrectly, but dont know enough to determine this. Anyone have an idea?