Out of curiosity, who were they most racist against?
I think that Korea has historical/cultural/geographical reasons to basically be prejudiced against both the Chinese and the Japanese. A lot of old wounds and mistrust there.
I also think that people from "northern" Asia commonly harbor racism towards people from "southern" Asia, i.e. the Thai, Laotian, Cambodian, Vietnamese, Malay, etc. There are some who think Southeast Asians are lesser.
I haven't seen a lot of outright racism against Euro or American folks from the Koreans I've known... Although when I was drinking until 3 AM with the sales/FAE team from Korea in Vegas at a work convention it might have been because we were all hammered and they were impressed I had a second degree black belt in Hapkido and could count to 10 in Korean... So maybe I'm just "one of the good ones" lol...
They hate the Japanese most, that is for sure. So much so that my friend could hardly say the word for "Japanese" without curling his lip. And the word itself sounds ugly--"Il-bon." I don't think that there's even a connotation of "people" in that term. As I recall, "saram" is "people. Americans are "Mi-guk-saram."
They have a love-hate sort of thing with China. I remember hearing a joke about a Korean, a Japanese, and a Chinese being put in the same dungeon. I can't remember the gist of it, but the bottom line was that after some number of days or weeks, both the Japanese and the Korean pleaded that they would gladly stay in the dungeon if the authorities would just take the Chinese guy out. OTHO, they are to a significant degree proud to be part of "Chinese culture."
They don't like mixed-race people. I had a U.S. Army officer who was part Japanese, part Chinese, and part native Hawaiian as a roommate for about 6 months, and my colleague and friend Captain Hahn (ROKA) really had to work to consider the "Asian mutt" as something acceptable.
They don't like it when Korean women marry American GIs, most particularly if the American GI is black. Maybe they picked up that last part from us. That's one of those things that it's hard to ask a Korean friend about because he probably won't admit it and probably wouldn't know the answer if he would admit it.
The Japanese still discriminate against Koreans. It didn't end in 1945. And the Japanese even discriminate against Okinawans (who are legally Japanese) too.
I didn't encounter ill feelings towards South Asians, but then the subject never came up. So I have no knowledge one way or the other on that.