BTW, I just played with the "Add Layer Mask" dialog (would you believe I'd never used the menu command?) and found a way for that to work, too.

If you want to add a layer mask that is white like I do when I click on the shortcut icon, you would choose "Add Layer Mask -> Reveal All." That adds an all-white mask to the layer that you can then work on.

However, if what you want to do is apply something to just a tiny bit of the picture, you COULD choose, "Add Layer Mask -> Hide All" and that would add a black mask to it. Then you could paint with a white brush or white pencil to show just the parts you wanted. I hate to keep going back to that palette illustration, but please look at it again:

http://pics.livejournal.com/hsapiens/pic/001t5x6f

You see that selective color layer up near the top? That was me making her lips a little redder without making the whole picture redder. Adding a "Hide All" mask to that sort of layer would just be quicker than what I've been doing, which is blacking it out with a huge black brush and then painting on it in white. Hope that makes sense.