Despite me having some (many actually) issues with the show's writing and logic one of the few things I can actually appreciate in Tale of the Nine Tailed Season 1 is how Yeon and Rang subtly reflect or share their colours. It’s often shown that they both share or wear each other's colours, like they're tied together.
Yeon’s is mostly red, Rang’s is mostly black.
Yeon’s fur is mainly red with touches of white, while Rang’s is mostly black with hints of red. Their fox fur colour are shared with each other at that time as red at the start.
Even when their hair was long Rang's hair tip colour was red and overall black and Yeon's hair tip was white and overall red. Like even in natural state they share the colours one way or the other with red mainly at that time.
However in modern times after everything went down, with distance and cutting their hairs short instead of sharing we see them often wearing each other's colours that reflect each other.
Like one way or the other they're sharing or reflecting each other colours. And it's really adorable honestly since they do it unconsciously with the red and black!!!
Don't tell them that though lol they'd deny that till they're blue in the face.