This exercise can be solved using the following functions:
Selection Tools, Selection Types, Color Balance
Save the picture color.jpgto your folder and open it in Photoshop.
Use a Selection Tool to carefully select the iris and pupil of an eye on the girl to the left (that’s the “inside” of the eye, the ring of color and the black dot).
Now set the Selection Type to Add To Selection and select the other eye as well. Read more on Selection Types under Selection Tools: Basics and Fancy Tricks in the Tools chapter.
Use the Color Balance function to change the color of the girl’s eyes. When you’re done, turn off the selection by Deselecting it.
Repeat this procedure with everything in the picture. Use different Selection Types on your selection where it fits. When you use Color Balance, try switching between Shadows, Midtones and Highlights. This will give you some very different results.