i love gimp.
ive been playing around with it for a couple weeks now.
im a little addicted.
its free.
i think its equal to photoshop. honestly, i like it better because im more familiar with it.
download it here.
you can mess with color:
*edited*
*original*
sharpen dark photos
*edited*
*original*
just go to google and look up gimp tutorials, youll find all kinds of info. how to antique photos, darken edges, lighten photos, airbrush, hues.....etc......awesome