Eyes are definitely something you should consider, unless your OC has eyes like the Gravity Falls characters, where eye color doesn't matter/doesn't exist. There are three things you should probably consider when making your OCs eyes; eye shape, eye color, and eye differences if they can possess people, shapeshift, or not. I'll talk about all three of them for ya!

Eye Color

If your OC is a normal human, then you'll mostly focus on eye colors above eye shape and different eye looks. Brown, green and blue are the most common colors, but there can be gray or other colors I fail to mention (especially if your OCs wearing different colored eye contacts). But there are exceptions! Some people can have two different colored eyes, called heterochromia; my eyes are both brown, but one is slightly lighter than the other. Some people have one brown and one green eye, or one blue, one brown; one brown, one blue, etc. (If your OC is a mutant, like the X-Men character Mystique, then you'll defiantly have to think hard on their eye color).

Eye Shape

If your OCisn't human, (and has different eye colors then a normal human), then maybe you'd want to focus on the shape of the eyes, make them unique. Most human eyes are shaped oval like, or round if your OC is in a animation tv series (like gravity falls); your OCs eye shape could be squares, buttons, a eye patch, just to name a few. Not everyone has both eyes, or normal eyes for that matter.

Eyes When Possessing Someone/Shapeshifting/Superpowers

I'm going to use Angels and demons from the Supernatural series, since they are some food references for this topic. When a demon possesses a person, that person's eyes turn from their normal color to black, red or white; when a angel possesses a person, that person's eyes turn from their normal color to a bright, glowing blue.

When someone shapeshift, like Mystique from X-Men, there eye color and shape turn into the person/being there shapeshifting as. If your OC can shape shift, I suggest giving them a eye color that would be unique to them, like yellow or purple or red.

Sometimes when someone is using superpowers, like Jean Grey (The Phoenix from X-Men), her eye color can turn from normal to bright orange, often looking like fire. Depending on what your OCs powers are, you might wanna consider matching the colors of your OCs uniform/powers with their eye color.