In this sentence, "xanh lá" is not "green". It's a fun way that Vietnamese people used to play with words. Sometimes they don't want to go straight to the problem, they use another way to say that word, but with condition that the speaker and the listener, both understand the meaning of this word. Back to the problem, in this sentence, it took me, a native Vietnamese speaker 1 or 2 seconds to translate "xanh lá". And the result must be "xa lánh" = "stay away from me". Those days, people used to speak like, for example: 1/ Nhìn là "hốt cả hền". hốt cả hền = hết cả hồn. 2/ Muốn đi ăn phải không? OK, "đầu tiên"!!!! Above sentence, "đầu tiên" is not "firstly". It means "tiền đâu" = "where the money is?" There are thousands of slang words in Vietnam, I can not count ... Tip for you: Try to speak the word out loud, and try to speak the word in the many different orders, if you are not an native speaker and you're lucky enough, you might find out the meaning of the word.

Xanh lá là tính từ, mình không hiểu câu trên của bạn lắm

It is a slang - fighting to the end

I think it is an metaphor in Vietnamese. But I never hear about it. This sentence can come from a paragraph, so you need considering the whole those content.

Ah....So..You mean that is not a word. it is a fake word. Thank you for answer.