Danik
Yes, you can do this by holding Shift when picking the color.
Add shortcut to colour select on current layer
G
Grofit
I tend to use a layer for shading and use alpha on it, then that way I do not need to worry about messing around with shading on each layer, problem is when I want to edit that layer and I go to colour select it picks up the underlying colour not the colour on that layer (as its transparent).
So it would be great if you could use alt + ctrl or something to imply that you want the current layers colour not just the displayed colour.