I am currently at chapter 60 or so, and I am wondering about the use of color in this comic: as far as I can tell, red represents Mian's psychosis, as it only ever pops up whenever Mian slips into her deranged avenger mode and starts alternating between injuring Haegu and demanding sex from her. Blue, meanwhile, represents blood and gore, but also some aspect of Haegu's character that I cannot quite put into words yet. Anyone has any ideas about that? I've also noticed that sometimes when Mian and Haegu get it on, the red and the blue mix into purple for a bit.
About the colors, it's as you said, red is for Mian whenever she sees things, like haegu or her dad playing with her mind, it also shows up when Mian gets deranged, or demanding, her eyes even turns red when she's in that state of mind. Meanwhile Haegu represents blue, her eyes will turn blue too in the upcoming chapters when she's in a deranged state of mind.
As for blue and purple for bloody, gore and bruises scenes, I think it's just to make the scenes look less disturbing, I think the scenes would look way too disturbing if they showed up blood and bruises in red.
So I have caught up with the latest chapter and have more thoughts on colors: Blue seems to represent what I call "hitman psychosis" -- the extreme desensitization to violence and death that hit(wo)men in this series display (which may be linked with the stylistic choice to represent most blood as blue, as well). This is why Haegu is so often blue-coded -- she is most commonly in that killer mindset. Simultaneously, however, Mina Park, the prosecutor, is also often blue-coded even if she never harms anyone, so I guess blue can represent general adrenaline rush, since Mina is often in danger herself?
Red is clearly Mian's psychosis talking, except when has hallucinations of her dad, who is blue-coded, because he was a hitman. Interestingly, when Mian cuts herself, her blood is the only one in the entire series that is properly red. Presumably because her self-harm is an outcome of her psychosis.
Finally, purple (a mixture of red and blue) is obviously Haegu and Mian's respective psychoses canceling each other out when they are together, allowing them to behave like a normal couple as long as nobody tries to kill them. It's interesting that whenever their relationship manifests itself in kindness, there is always at least one purple item on the screen, like Mian's scarf, or those headphones, or even blood on Mian's face after Haegu took care of her.
Lastly, there is green, but there is so few of it, who the heck even knows what it meant.