USING ADJUSTMENT LAYERS TO CHANGE HAIR COLOR
You have a friend who has decided to dye her hair but can't decide which color. Being the friend
that you are, you use your mastery of Photoshop to give her some samples to choose from:
Add a solid color adjustment layer
Image adjust>invert
Paint in the hair
Change the layer opacity
Save the image.
Double click on the adjustment icon, choose another color.
Save and repeat until you have five different samples.