using PS 8.
PART ONE: Eye Coloring
step 1: Do whatever with your base. Sharpen, etc. I especially like to use the dodge tool set on a low-medium exposure to brighten the eye. I did that with my base, as you'll see. (Nobody has eyes that bright! XD) Duplicate the base, and set it to soft light 100%.
step 2: Create new layer. (layer > new > layer) Use the brush tool set on size 7, 100% opacity to paint over the iris using #00FF2A. Make sure not to color over the whites of the eyes, or to color over the skin. Go back with the erase to get all the extra bits. Set this whole layer on Hue 100% opacity.
step 3: Create another layer. Use the brush tool set on size 3, 100% opacity to paint the OUTER CIRCLE of the iris a dark green. (I used #002A07.) Keep this set on 100% opacity. Now take your blur tool, set on 100% opacity, size 7, and go over the dark green circle to make sure it's nicely blended, but still prominent.
step 4: Create yet another layer. Use the brush tool, this time set on size 5, still 100% opacity, and paint a small INNER CIRCLE, close to the pupil, with a light green. (I used #23B73C.) Set this one to soft light, 100% opacity. Take your eraser tool, and change the size to match roughly, or perhaps a pixel or two larger, than the pupil (the black part). Now click once or twice with the eraser over the pupil. Do this ONLY on the layer with the light green inner circle. Flatten the image, go over the iris with the dodge tool, set on size 10 and 25% exposure.
PART TWO: Makeup
step 5: Create a new layer. Use the brush tool set on size 7, 100% opacity to paint around the eye with pure black. Set this layer to soft light 100% opacity. Go over the edges with the blur tool set on size 8, 100% opacity.
step 6: Create yet ANOTHER layer. This time, set your brush on size 3, keep it black. Paint a thin line all the way around the eye, on the inside. Leave this one on normal. Blur it with the blur tool, set on size 3, opacity 100%. Flatten the image.
step 7: Duplicate the image twice. Set both on soft light 100% opacity. Go back to the base layer and desaturate. Done!
(this tutorial was created using a picture of my own eye.)