For this tutorial, I will be using Photoshop CS3.
Any colored portrait will do.
Step 2: We will begin with the eyes, as they are the easiest to do. With the polygon lasso tool (L) set at feather: 0 outline the eyes. Zooming in to about 500% will help a lot. You can zoom in by hitting Ctrl + on your keyboard. After the eyes are selected, create a new layer by going to layer - new - layer and fill them in with another color. I will be using a brown with a green undertone to give dark hazel eyes.
Step 3: Yes, this looks completely fake and unnatural. Don't worry we aren't done yet. Now, set that layer to multiply 80% or whatever looks best with your image. I find that multiply 50-85% will look best - just depends on how intense the new color is.
Step 4: You can use other colors but subtle colors will look the most natural. Below are some more dramatic colors:
Step 5: Now we will change the lip color. Outline the lips just as you did the eyes with the polygon lasso tool (L). After that, create a new layer and fill it with the another color. I will be using a hot pink to give a darker hue to her lips. I set this color to multiply 50%.
Step 6: Now you can just zoom out and make sure everything looks good. You can change the fill percentage of your new color layers to adjust any last minute touches. Thanks for reading my tutorial. Happy editing!