This is a free program that I used when taking pictures. It has the ability to darken or lighten a different zone of a picture. A zone is a different shade ( luminosity ) of any color in the picture whether it is connected or separated from other zones, of the same luminosity, in the picture.
I just took a quick look at this. I think I like it. I have gimp, but i am so rusty at image editing it hurts.