Don't know if you're on Blab or not, but there's a thread there about painting eyes.
I've copied some of the responses here so you can see how some other people do them.
Jaime B:
Horses pupils are elnogated and horizontal for starters, not dots or round. How I do my eyes, is I start with a bit a pale pink for the eye corner and sclera. Then I go around what would be the actual eye and paint that in black. Then I go for a darker brown and do the iris, leaving a tiny black rim around the outside of the eye. Then I blend a lighter brown towards the center. Then finish off with the pupil. I go back once the entire eye is dry and take a dark blue colored pencil and put a reflective blue inside the pupil. Then I use a matte sealer. Then, the last stage is a gloss. I use any glossy nail polish but some people use liquid resin and some other things. But you must make sure you use sealer on your eyes before you gloss them or the gloss will remove the paint.
PA Gershler:
Mine are pretty basic. Paint the whole eye unbleached titanium (it's a nice cream color), then go over it with paynes gray (a nice blue-black-- sometimes I mix in a little interference blue), leaving only a smidge of unbleached titanium showing (eyewhite). Then I go over the paynes gray with a mix of burnt umber, metallic copper, and interference gold, leaving a small rectangle of paynes grey in the middle, and a rim of paynes gray around the outside of the brown mix. After that, put a titch of flesh tone pink in the corner of the white and Voila! Eye. After the last layer dries, I seal it with matte, then gloss with clear nail polish. HTH!
Melissa Mistretta:
For sclera (eye white) and other non-iris eye detail, I use the following colors:
-A mix of artist-quality white and burnt sienna to get a pinkish-white color, add to this a tiny drop of burnt umber to tone it down a bit so it's not bright pink.
-the Ceramcoat color Dark Burnt Umber
-Burnt sienna toned down a bit with a little burnt umber, add a tiny drop of white to lighten it just a tad.
I mix up all three of these colors on my palette (usually an unwaxed paper plate for eyes!). Using my eye brush, which is a 00 Taklon liner with medium-long bristles, I water down the white/pink mixture a bit so it's slightly thinner than cream. I paint the entire eyeball in this color and let it dry. Next I thin down some more of this color, but not quite as thin as before, so it will not dry as quickly, and dab it into the area that will show the whites of the eye (a note here: just about every horse I do shows at least *some* sclera. I find this gives them more expression). You do not have to paint the entire eyeball again with this thicker pink color...just where you want the whites to show.
Now, using the same brush, I thin down the burnt sienna/darker pink-brown mixture quite a bit so it's very thin. As you're cleaning your brush and thinning the dark pink, the paint you just applied will begin to dry a bit and gel up somewhat. When the dark pink is quite thin, turn your brush so it's sideways, almost parallel with your plate, and roll it between your fingers as you draw it out *away* from your thinned puddle of pink paint. This will form the bristles into a nice, sharp tip and will also get the excess watery paint out of them while still leaving more in the bristles than you would if you blotted it on a paper towel. Put it back into the paint and roll it out again, a few times, until you think it's nicely loaded with your color, has a nice sharp tip, and most importantly, won't drip any big globs of watery paint onto your eye. If you've made some little squiggly "tentacles" of paint come out of your puddle that dry very quickly, you've done it correctly!
Take it back to your eye now, and moving from the centermost point of your fresh sclera paint out toward the eyelids/corners of the eye, very gently dot the watery dark pink into the still-wet-but-not-yet-dry light pink. Don't overdo it...you just want to put a few splotches of dark pink coloring about where the edge of the iris will be. Now, if your eyewhite will be at the frontmost corner of the eye, dot a little of this dark pink color into the forward corner of the eye to color the lacrimal duct (that weird lumpy thing you see in your own eye, that's in the corners closest to your nose).
Now quickly clean your brush, and again water down your dark burnt umber paint. Quickly load up the brush the same way you did for the dark pink. Now you'll carefully paint a little line that goes all the way through your sclera. It should be about halfway between the lid/skin and where the pupil will be. You will probably find it easier to make the line in a series of tiny, connected dots than by swiping the brush. This is your haw, or third eyelid. By now your sclera area looks awfully crowded with a pinkish-white color, some darker pink splotches (that by now have probably bled a bit into the light pink), a lacrimal duct (if you're painting the front corner) and the haw. That's okay, it'll look really cool when it's all done.
Now rinse your brush and blot it so it's a bit damp, and with just water, gently dab at the eyewhite area so that it smooshes your haw line around a bit and forms it into an even thinner line. This takes some practice to manipulate the light pink paint with your bristle tips and shape the line without obliterating it or blending it in. This is why you're using watery paint on top of thicker paint...they dry at different rates, and so you can preserve the haw line easier that way. Once your sclera details are how you like them, you're ready to move on to the iris.
Brown irises:
-Ceramcoat dark burnt umber
-Black
-Creamcoat Spice Brown
-Artist quality burnt umber
-Artist quality metallic copper (Liquitex makes a bottled one that works well!)
-Artist quality burnt sienna
-Artist quality ultramarine blue or interference blue (ultramarine tends to work better for me)
First, paint the shape of your iris over your *completely dried* sclera, using a well-thinned coat of either black or dark burnt umber (I like the dark burnt umber, myself). Obviously you'll want to leave the sclera details you just spent so much time on! Let it dry well. You should now be able to see the basic "feel" of your eye...your sclera and haw will be showing in all their detailed glory, and you will have your iris roughed in, giving you a taste for the personality of the piece.
Once your iris background is dry, get some spice brown, copper, burnt umber, burnt sienna, and black on your plate. Because of the way light refracts from the curved cornea, the upper half of a horse's iris generally tends to appear darker in color (in most lighting situations) than the lower half. So water your spice brown down to somewhere between the wateriest paint you've used in painting eyes, and the thickest you've used. Paint a little smudge of this color along the bottom of the eye. Don't make the edges of this color go all the way to the edges of the iris on either side...you'll want to leave a little border of your dark color.
Now take some burnt umber. Mix in the teeniest dab of burnt sienna so it gives it a warmer tone. Water this down to the same consistency as the spice brown and do the same technique across the top of the eye...a smudge with dark borders on either side.
Now, clean your brush out, and blot it so it's damp. Using a very gentle stippling motion in which your bristles barely even leave the eye, blot the light tone up into the dark tone. Your paint will begin to dry at this point, so I recommend you do either side of the eye first, carefully keeping the border of the iris intact, and then the center. With a slight dabby motion, move your brush slowly up from the light into the dark, and then back down. Just do enough to get the colors to fill the empty space between, not enough to blend them all the way together. You should produce something vaguely flecky and mottled. If you feel the color is too dark or too light, pick up a little of the opposite color on your brush and work it in to brighten or darken the eye. You want to preserve a general darker tone above and a general lighter tone below. KEEP THE BORDER OF THE IRIS INTACT! Work very carefully around the border. This is why working with creamy paint, neither too thick nor too thin, is important.
Now pick up some pure black on your brush. Get it fairly watery and do that twisty brush-loading trick as you did for the dark pink splotches in the sclera. Starting in the center of the eye, make quick swipes here and there out toward the edges of the iris. Don't actually go all the way to the edges! And don't do too many. You want to hint at radial striations in the eye, not actually paint each striation! Don't make the striations too short either, or your pupil will blot them out.
Let the whole thing dry thoroughly. Now it's time to paint the pupil!
Make your black paint fairly watery, but not super-duper watery. Paint your pupil on, keeping in mind that horse pupils are horizontal and sort of roundy-rectangular in shape. I generally achieve the right shape by painting one bold swipe across the iris, and then gently humping up the top of the rectangle a tad. Just a bit! You'll want to put your putil where it would be in the center of the *iris*, not the center of the eyeball. This means if your horse's eye is rolled very far, you might have some or even most of the pupil very off-center and perhaps even covered by a lid or an eye corner! Use your discretion...just remember that pupils go in the centers of irises.
Once your black has dried on the eye, water it down more and pick out a couple of striations by gently streaking *thin* little lines of black out of the pupil. Really watery paint and a nice, sharp bristle tip should keep the lines plenty thin enough. If your paint isn't coming off the brush with just gentle strokes, load it up a bit more with nice, watery paint and really point that tip. don't press harder...your lines will be way too thick. When you have your striations how you like them, water down the copper well and highlight the lighter areas of the eye with a few gentle streaks or splotches. You can even put a small speck or two of copper in the dark area of the eye.
Finally, water down your ultramarine blue well and paint a dab in the middle of the pupil. Blot your brush completely dry and gently work the blue so the edges of the dab soften up and blend into the black. This makes a realistic lens reflection off the eye. It shouldn't be noticeably bright blue, or your horse will look like he's going blind. It should just be noticeable in certain lights. If it's too blue, wash over with with watery black.
When your eye is totally dry, spray the horse's face with a coat or two of Dull-Cote. when that has cured, give the eye a coat or two of high-gloss clear nail polish. I use an old liner brush to apply this and work it into the corners of the eye.
BLUE EYES.
Okay. The method is actually very similar to painting the brown eyes, except for differences in color. I use the following colors and mix them in various ways to make the appropriate shades of blue:
-White
-Ultramarine Blue
-Pthalo Blue
-Ceramcoat Ice Blue
-Spice Brown (mixed with blue shades, it gives a nice earthy-green-blue tint that is very handy sometimes!
-Black (mixed in a teeny bit to give a more grey-blue shade
I use a mixture of pthalo blue, ultramarine, and black to make a very dark, near-black color for the first step of painting the iris - what will eventually become the border - for most blue eyes (very light blue eyes, like those on splash white horses, I add a dab of white until it's a lighter, but still dark, shade). I mix up a very light shade of blue, usually mostly ultramarine and white with a touch of pthalo, or straight ice blue, for the lightest shade (the spice brown step in brown eyes). Sometimes I use white with just the barest touch of ultramarine and an even smaller amount of black, for a very light blue-grey...this is for the very lightest blue eyes. For the darker tone on the top of the eye, I lighten up the color I use for the background/border with some white until it's a rich medium blue. When you dab this color together with your very light lower color, you will get a nice mid-blue tone. For the striations, I use a color near to the darkest blue shade.
The pupil of blue eyes I paint black with a touch of pthalo, and then do the lens reflection in ultramarine.
I have not yet found a good metallic color that works well with blue eyes. I have had some success with mixing a touch of silver in with the lightest blue mixture and using this to highlight, but sometimes this doesn't work well at all. You might find interference blue useful for this step, or you can just leave it out altogether, as blue eyes tend to stand out well on their own.
Blue eyes bear a few notes before you paint them. First of all, just like brown eyes (although this is much less noticeable on dark-eyed horses), one horse with two blue eyes does not necessarily have two identicaleyes! They can and do have different-toned eyes on either side of their head, so don't worry about making both eyes match *exactly*. Blue eyes can often have brown flecks inside, or can be half-blue, half-brown. Blue eyes often have a greenish tone to them, especially true on ivory champagnes, so you might find a teeny bit of spice brown added to your blue mixtures helpful. Some horses' eyes are so light blue that they look almost white, and some are very dark...especially baby horses' eyes. Some horses appear to have greyeyes, and some seem to have turquoise-greenish eyes. Use reference pictures to help you gauge the tone.
I've copied some of the responses here so you can see how some other people do them.