He might just be eccentric, or it might be a modern form of dress. My mom was telling me all sorts of things about how she had observed Korean clothing traditions changing over time. For example, when she got married (mid-1970s), a bride wore a yellow jeogori (I hope I'm transliterating that right) on the day of her wedding and green thereafte. (Or was it that unmarried women wore yellow and married women wore green? One of the two. My Korean is bad, so I sometimes get these things wrong.) But nowadays brides will even get married in black-with-gold-embroidery, and Korea's been influenced by the West long enough that black = death/mourning is known. (Traditionally--well, for certain values of "traditional," probably meaning Joseon and my mother's childhood--you wore white for mourning, or an undyed cloth like hemp that was basically off-white.) All this just to say that clothing has been doing a lot of evolving. I wish I could make my mom read the manhwa and ask her what she thinks the clothing signifies, because I bet context would help.