Probably. It's still very much a mono culture. Since it's a "by Koreans for Koreans" industry there's really no motivation to have a dark skinned character in a Korean comic.
Also, Naver and Kakao focus on webtoons they think can get a live action adaptation on Korean Netflix or one of the national networks and the comics creators know this as well. It's a lot easier to find a Korean actor than it is a foreign actor who can speak Korean fluently. There's no financial motivation either.
Make no mistake though- Japan doesn't have dark-skinned characters because they're down with the culture. They fetishise black men and hip-hop to the same degree they do school girls. It's the same thing that gets white folk calling their comics "manga" and drawing like they're Oda.
Don't forget the American GIs stationed throughout Korea. In my experience they make up the majority of dark skinned people Koreans meet.