I think I know why people aren't coloring. ;D
Put the pupils and eye whites on another layer, but that layer has to be above the Lock Alpha. I noticed that I was coloring the whole eye, including the pupil n' stuff, not just the iris. :3
Also, put the lock alpha layer below the lineart layer, so you don't color over the lineart.
Instead of using white to block out the original face, just don't touch the original lines. The person coloring can easily go to the lineart layer and erase part of the lines. ;3
I think I might be a bit confusing... XD
~Kesh