To me, Japanese horror and Korean horror films share a lot of similar characteristics. I'm used to seeing a scary, makes-your-skin-crawl female 'ghosts' dressed in white with long black hair. However, ghost characters today don't follow the white clothing characteristic. I think the one reason why the 'ghosts' would be wearing white clothing is because white is color you wear to funerals. In Korea, the traditional dress in white is what you're supposed to wear. Therefore, a lot of ghosts would be wearing that white traditional dress to haunt you. I guess in a way, it's supposed to signify that she's dead. But, I'm sure the true reason why these ghosts wear white in horror movies are from history. Maybe in the past, people saw female ghosts with long black hair and wearing white clothing.