When you want to select a whole color area in PdN, use the Magic Wand tool and play with the Tolerance slider. When you get what you want, change Selection Mode to "Add" and click on multiple areas. Copy/paste to a new layer. Make your color adjustments and then apply a slight Feather effect - that will blur the edges of the selected area while keeping the rest of it intact. The blur will help it re-blend with the background a little better.
Thanks for the tips...I was already using the wand, but that's a new trick for me.
Part of the problem was relatively low resolution such that there was significant pixelization problems to overcome.
BTW: how do you "feather"?
Here's my applying as much of that tip as I could: