This is one of the most simple to perform that I've never seen for change someone's hair color in a photograph or to add highlights.
In CG Shelf they teach us how to do it with an illustrated tutorial with photographs that, although it is in English, You can go on perfectly without reading the explanations, just looking at the screenshots.
I hope to see your hair color changes in the forum Creativos Online
Source | Tutorial to change hair color or make highlights with Photoshop