What do the colors, Blue, Dark Grey and Red mean in Taylor Swift's song Red?

Question

Taylor Swift's song Red has following lyrics:

Losing him was blue like I'd never known

Missing him was dark grey, all alone

Forgetting him was like trying to know somebody you never met

But loving him was red

What do all these colors mean in the song's context, especially the part "loving him was red"? I am curious about what they represent.

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_{I am not actually sure about the tags, so I added the one I found appropriate for my question.}

Answer 1

Colors in songs are generally symbolic presentations of feelings or expressions. Darkness or grey represent aloofness, dullness, or sadness. Feeling blue means melancholy, but red is explained by herself -

Her emotions throughout the relationship, which she described as both the worst and best thing ever, corresponded with various colors — the chief among them being red.

"Red is such an interesting color to me because you have the great part of red," she said. "Like, the red emotions that are like daring and bold and passion and love and affection."

But red can also symbolize the negative aspects of powerful relationships.

Source: NYDailyNews

Answer 2

• Feeling blue - feeling depressed and sad
• grey (by extension) another sad feeling, dark grey is similar to black: Beatles: Baby's in black and I'm feeling blue
• red is color of passion