This is the edited version of the previously finished image. The eyes and hair colors are changed.
The following image show the photoshop interface demonstrating this process.
New hue/saturation adjustment layers are added (Eyes and Hair layers). Then, the desired colors are adjusted using hue, saturation and lightness levels with colorize option. At this point, all the image is filled with the color. The layer is then filled with black color to hide the colors. Next, a white brush is used to reveal the color back at the desired location. For example, the eye color is revealed by brushing the pupil area of the person. The blend mode is also changed to color (for the eyes) and soft light (for the hair) to only change the color, not the brightness. That’s it! The colors can always be changed at the properties tab showing hue/saturation/lightness.
These steps are found via Google in photoshopessentials.com. These edits are relatively simple because of the use of adjustment layers. I would say that I would a bit more likely to remember these processes if it is demonstrated in the class.