Actually the korean and chinese eyes look similar, belonging to the Asian eyes. If you really want to distinct them, you could just choose to base on the languages they speak. The eyes color is really hard to make the distinction. The Asian eyes are just similar which will have no big obvious difference. You could base on the behavior or other things to make the distinction between them.
Well, I think you are very interested in such cultural or anthropological differences. As far as I know, Koreans and Chinese are very close to each other because China and Korea are geographically located not far from each other, what's more, during the course of history, Chinese have got a great relationship with Korean, which makes them not quite different, thus, their eyes are simply the same.