First you have to decide the color of hair. In this example the color of hair will be brown with a touch of gold in it. The darkest color will be nearly black.
Create a blank canvas with 200dpi.Make sure you don’t save your file in jpg format.
Select a neutral tone for a background that will suit the hair color. Fill the canvas with the color you have selected. Shortcut for Fill is Shift + F5.
Create a new layer and start blocking the shape of hair. Decide where it is going to start and where it is going to end up. You can afford to scribble without lifting your pen.
Refine your shape. Put a few crushes on the edges to make it look natural. It is always better to work in Photoshop with a pen and tablet set on size, not opacity. Those who work with a mouse might have to play with settings to find something you like.
This is a step where you can start making a palete. Lighten the half of the hair starting from bottom, just barely. Don’t use Dodge tool! There are many ways to lighten the hair, but I have used Hue/Saturation. First, roughly select half the hair using Lasso tool then hit Ctrl + U or go to Image -> Adjustments -> Hue/Saturation from the menu bar. Once at the Hue/Saturation window, select Colorize option . Now play with the slide bar to get the desired result.
Now you have two different hues on your canvas, go to color selector and pick a lighter shade of yellow color , and a shade of the brown. Select lighter color with a very small brush size and start bringing it up into the darker one and vice-versa. Now lighten the lighter areas, and darken the darker areas. Leave the darker areas near the roots; it’s where new hair grows from and thus hasn’t had as much exposure to the sun, and also the place where artificial highlights grow out.
Make sure you see the darker parts of the hair are from the last step.Go to color selector and select a dark version of the brown you have as your shadowed areas. Set your brush opacity to 60% and enlarge it to near 20 pixels. Darken the already dark areas. Don’t create new ones.
Lower the sizeof your brush down again to the 3-pixel area and go over the middle of the parts you just deepened to make them the darkest you have.
Click Select at menu, go to Color Range .This will open up a window with a sliding bar that says Fuzziness and a black and white window with a dropper. Select darker browns with the dropper. Now set the Fuzziness somewhere in the 20 -30 area or until all of your shaded areas are on the little black and white window. Now press OK and you’ll see that it selected all of the areas on your hair that are within a certain range of the color you chose.
Open the Hue/Saturation window or press (ctrl + U) and click the Colorize checkbox again. Now select the daker color ,say purple. Hit OK.
Using the Sponge to desaturate and Burn to darken, make the purple of last step look more dull and blackish. Darken the all dark areas.
Now its time to put some hightights. Go to color selector and pick out some lighter, desaturated (close to gray) orange and blue colors. Sharp hair will look unnatural. Use soft / fuzzy brushes in the back part.
Time for finishing touches. Pick a light yellow color and set your brush to 60% opacity, very small brush. Look for the lightest spots and touch these up with the light blonde to really make them stand out.