Korea has little ethnic diversity. I’m married to a Korean, and when we stay in my relatives’ hometown, I definitely stick out. Old women and children stare. Blue eyes really catch attention. But people are friendly.
Like even said, there’s a certain “celebrity” to being a foreign. I’ve had school children come up to me multiple times to try out their English. Random people on the street have given me local fruit or street food so I could try their food. Camera crews doing local news will linger on me (this is almost creepy, but there’s no ill intent, just curiosity). I’ve gotten large discounts at little parks and temples. Free souvenirs, too. The attitude is a combination of intense interest and hospitality.
Of course, that’s only in the back hills. In the Seoul megalopolis, foreigners are common. No extra attention there. You’re assumed to be just another soldier or missionary.
While Korea is homogeneous, it’s starting to change. There are some immigrants working low skill jobs, but not many yet. Domestic Korean labor is cheap enough that foreigners can only compete in the most dreary jobs. The real change is coming because of a demographic problem: Korea has significantly more men then women. This is due to their Confucian culture valuing boys more than girls, and it has affected their birth ratio (the exact mechanism is controversial).
Many poorer Korean men (especially farmers), who can’t afford a Korean wife, will import a bride from the Phillipines, Vietnam, or Thailand (Buddhist countries have a better sex ratio). The wife basically integrates into Korean culture, but it’s not without hassle or controversy. The government has special classes for foreign spouses, to teach them the cultural norms and cooking. I actually had an offer to attend one, but since I already know how to cook Korean and have no intention of learning the proper way to bow to my elders, I opted out.