Is there any difference between 绿 and 青?

One day, my DH asked me what’s the difference between 绿 and 青, when to use which. I realized I don’t really know. So I did a bit of research and this is what I found.

绿 = green = 黄色 + 蓝色  (colour code: #009000)
青 = cyan = 绿色 + 蓝色 (colour code: #00FFFF)

Cyan is between green and blue; it’s lighter than green, and closer to blue. That’s way 青天 is sometimes used in Chinese literature to refer to the sky.  The dictionary also explained that the idiom “青出于蓝” originated from the traditional way of extracting 青 (dye colour) from a grass called 蓝草. So now the idiom makes sense, since 青 comes from 蓝.

Extracted from Times Advanced Chinese Dictionary (时代高级汉语词典):

青天
【解释】:蓝色的天空。

青出于蓝
【解释】：青：靛青；蓝：蓼蓝之类可作染料的草。青是从蓝草里提炼出来的，但颜色比蓝更深。比喻学生超过老师或后人胜过前人。

I never knew that!  I’ve been using 绿 and 青 inter-changeably. I believe many people are doing that too.  I would say, generally, when it comes to describing the nature (tress and plants), 绿 is the word to use.

Here’s some 形容词 and 成语 that uses 绿 and 青:

“绿”字成语
    
绿叶成荫           绿草如茵           红花绿叶           红男绿女           花红柳绿
红情绿意           红红绿绿           大红大绿           灯红酒绿

“青”字成语

青梅竹马           青黄不接           青云直上           青出于蓝           青红皂白
青史留名           平步青云           炉火纯青           四季长青

“绿”字形容词

绿油油的…        绿色蔬菜           绿叶                  绿化环境           翠绿的…
绿莹莹的…        深绿                  浅绿

“青”字形容词

脸色发青               脸青唇白               青葱的…