There are times you'll need to change the color of something and messing with the color balance or hue and saturation just won't cut it. It may require adding a color layer and overlaying it to find the look you want. Doing this means you can change things like hair color, eye color or even skin color. You want the end result to appear as natural as possible.

I made this cover a while back for a user here on Wattpad

She requested that the model's skin color be purple. the skin color was a must for the customer.

I found the image of the woman first and removed the background, then I found a purple image and clipped it to the PNG of the woman. I played with the blend modes until I achieved a look that made it appear her skin is purple. I added a layer mask and erased the purple from her eyes, eyebrows, nails, and her bracelet.

You don't want this to happen

The poor woman is a solid orange blob. The color is awkward and there's no definition in her features. 

In order to make the coloring appear more natural you can mess with the blend modes to find the look that works for you.

The poor woman still looks like an Oopma Loompa, but now you can see her features more clearly.  You'll also notice in both images I erased the orange layer around the grass so it shows. If I didn't then the grass by her legs would have been awkwardly colored. The details matter.