Doyun has kind of grayish ahir parted in the middle. Dojun (the brother the doc is after) has a mole under his eye and black hair. Doha has curly/fluffy (im guessing thats what they're going for) hair. Taehan has short, black hair. I get confused between Doyun and Taehan a lot, so I mostly focus on the hair first for recognition. I hope this helps!
Thank you kind stranger!! ε=ε=(ノ≧∇≦)ノ
You're welcome! Sorry for the weird spelling errors. Auto correct corrects my Korean, but not my English. Lolol.
Im actually confused because of who's who, I mean they all hot but they kinda look the same hehe(￣∇￣")