A friend of me, Rahul, came up with this idea. He thought it would be cool to turn a "white" girl into a "black" girl ;) It's a very funny and creative effect and you can also try to use it the other way around!
Step 1
Get out your "white" person, since where're gonna change the skin tone!
Step 2
If you have a lot of trouble selecting the body, just create a new layer and brush everything that is skin in a desired color
Step 3
CTRL+left click on the thumbnail of the layer you just made and select the photo and press CTRL+C and CTRL+V and delete the red stuff;
Now press CTRL+U on the copied skin layer and add these settings
Step 4
Now select the lips and add these settings
Step 5
You can also add a small dot which is just a small circle brush...