Changing Eye Color
Open the photo you want to use to change the person's eye color. I am using the photo below I found online:
Use the zoom tool to enlarge the eyes.
On the image layer, use the Selection brush to select the subject's eyes. I used the elliptical selection tool and drug over the left eye first. To make another selection hold down the Shift key while dragging over the right eye. Making a selection will enable you to adjust only the color of the eyes.
Create a new Hue/Saturation adjustment layer above the image layer by clicking the create new adjustment layer icon on the layers palette and selecting Hue/Saturation from the drop down list.
Notice that the adjustment layer contains a mask filled with black and two white circles where you selected the eyes.
In the Hue/Saturation dialog box, check Colorize.
Play with the Hue, Saturation and Lightness sliders until you find a color you like.