What's the meaning of OUT OF BLUE here ?
When I saw the phrase , I thought it was used to describe something related to emotion.
but when I google it , it shows : suddenly .

“Well, this is out of the blue.” how do I know the meaning is "suddenly" or "depressed"

Does it have other meanings?

Question

What's the meaning of OUT OF BLUE here ?
When I saw the phrase , I thought it was used to describe something related to emotion.
but when I google it , it shows : suddenly .

“Well, this is out of the blue.” how do I know the meaning is "suddenly" or "depressed"

Does it have other meanings?

Answer

You can remember them with the reason or origin of the phrases.

- "blue" as melancholic or depressed:  The color feels cool.  It is the impression people get from the color.

- "out of the blue":  Think of it as "a thunderbolt out of the blue sky", which is something totally unexpected.  Hence the meaning "unexpected" or "suddenly".

Answer

OUT OF THE BLUE: suddenly, seeming to come from nowhere.

Examples: 
 
- The idea came to me from out of the blue.
- Out of the blue, a car approached.

BLUE: a sad mood or feeling

Examples:

- I'm staying at home today since I'm feeling a bit blue. 
- Rainy days always give me the blues.
- https://www.youtube.com/watch?v=SbJpzYHEnPI

Answer

I am feeling blue/ she seems a bit blue lately - depressed

Out of the blue - Suddenly. This phrase can not be said any other way. You will always see it in its full form as you do here.

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