tyrrant, I'll explain it simple:

First, you select only the bits that you wanna change. Then, you invert the selection, and copy those onto a new layer. You will have:

- pic with holes on the parts that you want changed
- base pic

Then, you create a colour adjust layer, just above the base layer. That way, it will change the colour of the whole pic, but then the topmost layer will correct the parts that you don't want changed:

- layer to mask what you don't want changed
- colour adjusting layer, making the fairy the way you want it to, but messing up the rest
- base pic: pink fairy, black background

If you want to e.g. change the hair to a set of colour and the dress to another one, there may be various ways of doing it. But I myself recommend doing it in two steps. First you do the step above with the dress, save the image into one layer, and then do the same process to adjust the hair.


Note that this is surely not the only way of doing it. Things like this are like a language: there are thousand ways of saying the same thing. You just need to know a bit of gammar and be creative.