Open Photoshop and load the photo on which you want to change the color of the hair. Click on the "New Adjustment layer" in the layers panel and select "Hue/Saturation" to adjust color saturation.
In the settings box tick on "Colorize" and set the saturation and brightness so that the result met your expectations. To preview click "Preview". Move the sliders until the color reaches the desired hue, and saturation.
After that, click "OK" and fill the black color mask adjustment layer ("Adjustment layer"). On the toolbar, select the brush tool and set the main color as white, to brush, to show a black fill color adjustment layer.
"Color" hairs soft brush of medium size to show color set in the above steps. More thin and transparent brush use for dyeing fine strands, increasing the scale of the pictures.
Set the "Blending mode" to "Soft light" to make the color of hair richer. If necessary, set the transparency of the adjustment layer and adjust the brightness and color saturation.
If you want to change the color of the hair, it is enough to click twice on the layer "Hue/Saturation" and using the adjustable sliders to achieve the color you need. To change the colors after you've created the layer mask with the desired parameters, you can as many times as you want.