How did the color "blue" be related to a sense of "depression"?
Yes, you're correct. This comes from the idiom "feeling blue" which means to feel sad or depressed. It can also be used to mean that you miss something or someone a lot or, to describe a of desperation because of sadness. Here, it seems Rose is saying that the person she loved has left her feeling depressed. Ex: You seem blue. What's wrong? Ex: I have been feeling blue ever since I have heard that my daughter will be moving abroad for good.
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