Note: I did this in CS5 but should be achievable all the way back to PS7
Step 1: Picking a Starting Photo
Step 2: Selecting the Eye
Then right-click and select "Choose Selection".
This will surround the eye with the spinning marquee.
Next click ctrl-J Or cmd-J on mac
this will Duplicate the eye.
Now click Ctrl/Cmd - D
This will deselect the marquee.
Step 3: Changing the Color.
Now the on pop-up, click ok. This will change the side tab.
Slide the color slider till the eye itself is the color you want. The rest of the image will change color too, but don't worry. We will fix that in a minute.
Now, if the color is not and "Colorful" as you want, change the saturation up. This will add more color.
Now, too save the color to just the eye, click ctrl/cmd - E
This will merge the adjustment layer and the eye layer. When you merge them, the color should only be applied to the eye.