Ok, well....let's say you wanted to make link's green color like a....blue.
So their is two options.
(make sure that you do NOT make ANY new layers)
1. Go to colors, hue and saturation, and chose green. Then slide the buttons to change the colors.
2. Free select the parts of his tunic, then click Colors, Colorize, and choose your color.
If have any more questions, just ask me!