Final
Original
Step 1
Go to Pen tool. Draw at the hair. If you did wrong just press Ctrl + Alt + Z
to undo.
then after finish press Ctrl+ Enter
Step 2
Go to Image > Adjustment> Hue & Saturation
Step 3
Setup the color with your own creativity. For Megan Fox Photo, I setup Hue +40, Saturation +26, Lightness -1.
Step 4
After change a color. Press Ctrl + D. If you looked smooth go to Smudge Tool to retouching at the color line.