Step 1 : Create the Duplicate Layer by clicking Ctrl+j

 Step 2 : Create a New Layer by Clicking Ctrl+Shift+N (Named Layer as Hair Color )

 Step 3 : Select the Brush tool  and Set the Opacity level 50% and Flow 100% and Hardness should be 0%

Step 4 : Select the Color Palet and select the color which ever you want.

Step 5 : Draw the Hair Color on the Image, You can Increase/decrease the Selection Tool Size by press "["  / "]".

Step 6 : Select the "Eraser Tool" and Set the Opacity level 50% and Flow 100% and Hardness should be 0%. Erase the Color which you feel more color on the Hair layer. That Image will look as below One.

Step 7 : Select the Hair color Layer and click the Adjustment Icon which is lying under Layer table and Select Hue/Saturation Option.

Step 8 : Right Click on Hue/Saturation Layer and Select "Create Clipping Mask"

Step 9 : Now Click on Hue/Saturation Layer, below window will prompt.

Step 10: Now you can change the Hue and Saturation and Lightness adjustments, will show you the Magic of color Changes....WOW.....COOOOOOOL....:)