In the Korean version of "The Tale of Chunhyang," this is the dialog between Mong-yong and Chunhyang before Mong-ryong revealed who he really was:
In the last comment of Chunhyang, notice the expression "초록은 동색이요," which I translated here as "Green is the same color." I do not remember how it was translated in the book I read, but if it were translated as "Green is the same color," I would have thought to myself, "That's a weird thing to say," and just included it among all the other weird expressions in the story. Now, however, I can appreciate the expression because now I know what "초록은 동색이요" means.몽룡: 너는 기생의 딸인데, 왜 본관사또의 청을 듣지 않았느냐?
Mong-ryong: “You are the daughter of a gisaeng. Why did you disobey the request of the official of this post?"춘향: 저는 기생도 아니고, 또 이미 지아비가 있습니다. 그래서 사또의 청을 들을 수 없었습니다.
Chunhyang: “I am not a gisaeng, and I already have a husband. Therefore, I couldn't accept the request of the official.”몽룡: 나는 지나가는 어사이니, 내 청도 거절하겠느냐?
Mong-ryong: “I am a passing Secret Royal Inspector. Will you also refuse my request?”춘향: ‘초록은 동색이요, 가재는 게 편’이라더니 양반들은 다 똑같은가 보우! 차라리 내 목을 베시오!
Chunhyang: “Green is the same color, and the crayfish sides with the crab, so all yangban seem to be the same. I would rather be beheaded.”
초록 (草綠) means "grass (草) green (綠)" or simply "green." It is a combination of 초색 (草色) and 녹색 (綠色), both of which also mean "green," so "초록은 동색이요" literally means "grass and green are the same color" or "This green and that green are the same color."
When Mong-ryong asked Chunhyang if she would accept his request even though she had denied the request of the other official, Chunhyang assumed he, too, was going to request that she sleep with him, so when she said, "Grass and green are the same color," she meant, "All yangban are the same," implying they all want the same thing.
In Chinese, "초록은 동색이요" is written as "草綠同色 (초록동색)," which literally means "Grass (草) [and] green (綠) are the same (同) color (色)."
By the way, the expression "the crayfish sides with the crab" (가재는 게 편) is similar to the English expression, "Birds of a feather flock together." A crayfish and a crab look similar in many ways, so one would expect them to take each other's side against an animal that looks very different.