At the end of the Western Han Dynasty, peasant rebels led by Wang Kuang, Wang Feng and others gathered in Dahongshan, Hubei Province, where the mountain was called "Green Forest Mountain". Because this peasant uprising triggered peasant uprisings in other regions, it finally overthrew the Wang Mang regime and produced the Eastern Han Dynasty. Later, people named the uprising "Green (Shandong) Forest Uprising". Later, people who gathered on the mountain to oppose the government were called "green (Shandong) forest heroes", and gradually the bandits who looted their homes also called themselves "green (Shandong) forest heroes".
Because "Green (lǖ) forest hero" comes from a place name, it can't be pronounced as "Green (lǜ) forest hero". It should be noted that the first letter of the "Greenwood Uprising" in history should be capitalized, because the rules of Chinese Pinyin stipulate that names should be capitalized at the beginning.
In addition, there are two places where "green" is pronounced as Lu.
One is the Yalu River. "Yalu River" is a transliteration of an old Korean saying, not that the river is as green as a duck's head.
The second is "green camp". In the Qing army, Manchuria, Mongolia and other ethnic minorities and some Han people were compiled as "Eight Banners" and called "Eight Banners Soldiers"; Han people compiled it as "green camp" and called it "Green Camp". "green camp" gets its name from the national flag, which is often green. Since it comes from green, it shouldn't be wrong to pronounce lǜ, but now the phonetic notation in the dictionary is L ǜ, so it's better to pronounce L ǜ.