Of course, the black eyes are the symbol of Asian people. You could buy the dark series contact lenses for your classmate. I think the dark black one may be the most suitable one that will make your classmate look charming in the eyes. Besides that, you could choose the dark blue ones.
Well, in my opinion, you can buy green or brown ones. Even if I have not worn them before, my friends who are Chinese people wear green ones and it makes them look beautiful. Also, you should avoid buying blue ones, for they can make the eyes unnatural and look weird.
If your Korean friend has yellow skin, you should buy her brown or black contact lenses for her. Brown or black contacts will make her eyes look bigger and more beautiful. If your friend has white skin as snow, it is better for her to wear purple or blue contacts which will make her look pure and lovely. Blue and white is just like the sky and white clouds and they are perfect match. If your friend has white and red skin, it is better for her to wear green contacts. Because green looks optimistic and vivacious. Gray contact lenses are suitable for people with different skins. Gray just makes you feel melancholy and immature.