"Green" is a reasonable translation - the same word is used for the "green" of plants or traffic lights. When referring to a mountain it is very likely to be referring to its greenery.
The boundaries between named colors have historically varied wildly between languages.
A fixed term which refers to the lushness and vegetation on a mountain. These are the precise denotations where the word is equivalent to English with "green".
And after a quick search, jisho.org translates that precise set phrase as "lush mountain; green mountain", though with an interesting alternate "burial place" meaning. https://jisho.org/word/%E9%9D%92%E5%B1%B1
And a couple of minutes later another quick search gives me a Wiktionary translation of the Chinese phrase as "green mountains; mountains with lush forests" https://en.wiktionary.org/wiki/%E9%9D%92%E5%B1%B1
The boundaries between named colors have historically varied wildly between languages.