when koogi hinted black hair!sangwoo might be a spoiler for s2, maybe she meant that we'll see him in a flashback?
I dunno it’s possible but at the same time ???Sangwoo’s current hairstyle has stayed the same for quite a few chapters so I would assume Koogi is going to just give him a new/different one overall in season 2. There’s also that theory saying he’s going to ‘change’ his friends so maybe it’s supposed to be a new him or something?