Sly is right, if you don't know how to make one, you could always have one made for you.
But I seriously love this idea. I was actually thinking about this a few nights ago.. because I don't have much time for presets anymore, and a lot of my characters have double eye colors. For example.. my character Fluxx, she has one green eye, and one purple eye. And I can make her find without a preset, so I feel it's not really needed for me to make a preset for her. As much as I agree with you Sly, I would love to see this added ingame.