Scan in the line art of your eyes into your computer or create line art in your painting program. Use the program to correct any mistakes of your line art before coloring.
Apply base colors to the eyes. Make the entire iris one solid color and the rest of the eye white. If your painting program allows, use layers to separate your base colors from the line art.
Add basic shadows and highlights to your eyes. Keep in mind the light direction as you shade. Stick to solid colors for your shading. Do not blend the different color tones of the eyes.
Lay your secondary shadows and highlights to enhance the picture’s look. Smooth and blend the edges of the color tones using the brushes and tools your painting program offers.
Finish coloring your eyes by adding any extra details and correcting any mistakes.