Well, this is exactly what I want... but without having to multi-click on color selector, color and "more>>".
Personally, I use Paint.NET (and I love it) more as a replacement for MS Paint than for a replacement of Photoshop, so I usually have just one layer and I need to do some "fast" editing, like resize, crop, save as and analyze colors. I don't think it should be difficult to implement this feature, since it is actually already implemented, but a bit hidden and cumbersome.