1. Draw your sketch. This part is fairly easy.
2. Fill in your base colors.
3. Change your line art color. To do this, I selected "Alpha lock" on my sketch layer and colored.
4. Add a gradient and mix the colors. I used the wet watercolor brush to blend the colors.
5. Blur the edge of the eye. Again, for this I used the watercolor brush.
6. Add a few tiny colorful dots around the eye. I used the splatter and stipple pen for this.
7. Add highlights. To do this, make a new layer above your coloring layers and set the blending mode to add. I used the pencil brush (set at 50% opacity) and made a large bubble at the bottom of the eye, then make some tinier dots around the pupil. I also painted some skin around the eye.