Showing, hiding and editing layer masks quickly
When you are working on a layer mask, rather than just brush randomly - it is often useful to actually see the channel/greyscale image that is making up the layer mask. When you select a layer that has a layer mask in, you will see it revealed as a temporary channel in the channels palette. Just as you can with any other channel, you can toggle its visibility here by clicking on the ‘eye’ next to it - by default it will be off. This overlays the layer mask ontop of oyur other layers. But of-course there is an easier and quicker way than keep on mousing over to the channels palette, which interupts the flow of your layer mask editing.
Simply hit the / key on your keyboard, which basically performs the same action as making the layer mask visible in the channels palette. If you hit it again, it hides the actual layer mask ‘channel’ visibility.
If you find the default red colour unsuitable for your work, or you want to alter the opacity of the overlayed visible layer mask, just double click on the layer mask in the channels palette. You will now have the option to change its colour when made visible. You can also alter the opacity - by turning the opacity up to 100% you can perform a final check on your layer mask so you can catch whispy light detail or any stray bits of your layer mask.
BONUS TIP
Its easy to save a layer mask, either as a working stage or as a backup. When it is visible in the channels palette, just drag the channel down onto the new channel icon and it will save it as an alpha channel.