So, this is for all the modern, edgy, punk youth out there. Or possibly weird, zany, old people. Basically, it's just coloring highlighter on your eyelids as eyeshadow. It's very cool. It brings out the color of your eye with he contrast. I tried it on my friend, and the only advise I can give you, if you try it, is to avoid rubbing it in your eyes!
If I were to ever make this idea into something, I would start by calling it EyeLighter. Get it, the play on words... Anyway, then of course, I would make it non-toxic and least harmful, but as close to a highlighter marker semblence as possible.
And to top it off, I would keep it in the shape of a pen, but maybe shorter and more compact, to make it easy to fit into a purse or pocket. Watch out! I see it in the future becoming the next new fad!