Yes.
By using the curves tool on a selection you can change the color to lighter or darker shade.
This is very, very, handy when trying to give an added or healed area of an image the same color shading.
For instance if i select a wire area in the image i want to remove or cover up.
I can then move that selection to another part of the image i like and copy>paste the selection.Now just make that copy and paste a new layer.Move the copied area over the area you want to fix and then use colors curves to fix the shading. If it's needed.Which it usually is. I have fixed many panoramas this way and older photographs.It's almost impossible to see the seams.

This bunch can never resist a challenge, submit one image or idea and get 200 responses, all of them right and different. This is good for even experienced users because it teaches old dogs new tricks. I think what really makes it good is that it never seems to be a contest.

Yeah, I love to have a go at these things but if somebody else can do better, fantastic. It teaches me something in the process.

+1 Erisian

Ok cheers Rod. My thinking was coming around to this as I'd hinted but via Adjust HLS. I'm going to set aside some time to work on my isolation chops as I still don't think I have it nailed and always have the dread feeling when I know I'm going to need to isolate an object, will be playing with the curves for sure

Gimp's curve tools are OK but I always feel I'm missing out on something are there any better (more powerful) curve tweaking tools around? (Maybe I should pull my finger out and learn to write plugins)

my experience is sometimes the cloner is too aggressive or uses a bit too much data than I need. In those situations I find it useful (though it takes a lot of work and time) to duplicate the layer and simply erase the object (takes a fine comb to do it properly) and then pencil in the background. For the air is it easy : colorpick from right next to the erased part.