This video shows "How to change eye color in Photoshop CS3"
First open the eye picture you want to change. Now select brush tool by
pressing "B" or select from the toolbar. Make sure there should be black & white color set in foreground & background. Now set "Quick mask mode" by pressing Q.
Now set brush size according to your size of your eye picture and hardness to zero. Now go round and round to your eye picture and color it whole but not the black thing in your eye but if you select it accidentally don't worry select white color in foreground and click that black thing in your eye it should get clear. Now get out of "Quick mask mode" by pressing Q button in your keyboard and go to "Select" menu and click "Inverse". Now see bottom of the layer window, you should see a half black/white circle, Hold down alt button and click on it and click "Black & white..." option now a new layer option pop up now click "Use previous layer...." and click ok this will pop up a new black and white option window, click "Tent" and move right and left the aero of "Hue". Now you can see the eye color is changing, set whatever you Want and click ok.