Recently I have noticed a sign saying “Brown is the new green” in the front yard of a house that I pass by every morning. This is the movement to encourage people to save water for the severe drought in California. Keeping your lawn green takes a lot of money, so it looks like an excuse for not watering to save, though it’s a reminder for others not to waste water just to make their grass look beautiful.
This reminds me of a Japanese saying: 隣の芝は青く見える (The grass is always greener on the other side). Literally translated, the color of the grass would be “bluer” in Japanese.
The “green” of the nature is often described as blue because, in ancient time, there were only four color terms in Japanese: black 黒（くろ）, red赤（あか）, blue 青（あお）and white白（しろ）. The color くろ (black) is related to くらい (dark) for something dark and shadowy, while its antonym あか (red) has the same origin as あかるい (bright), full of light = the color of fire. しろ (white) is also in the bright side of the color spectrum, but this color describes more about clearness or visibility. Then, あお (blue) takes the opposite side of the colors, not as dark as black, rather wide shades of grey, green and purple, including blue.
That is why “blue” is still used instead of green in lots of expressions in Japanese. For example, the mountains with fresh green leaves growing in the trees are called 青山 (lit. blue mountain), or the traffic light that indicates “go” is usually referred as blue, as in 信号が青になったら渡りましょう (Cross the street when it turns blue). Although, 緑 みどり (green) is also acceptable in the case of traffic light and actually used, still it is less common, partially due to the number of syllable being longer than あお (blue).
This color 青 (blue) has a connotation of being young, like an unripe, such as 青春 (adolescence, young days), 青二才 (greenhorn, young and inexperienced person). Yes, of course we describe those still “green” bananas as まだ青い (still blue), and even the green apple is 青りんご (blue apple).
So, in Japanese, “Blue is the old green”.