Blue represents both melancholy and warmth and gentleness. There are many kinds of blue, and each blue represents a different meaning. In addition, there are many examples of music, books and movies named after blue.

Blue source:

When he observed a 2500-year-old ancient Greek marble basin with a fluorescent lamp, he accidentally found that the blue pigment in the container began to glow-indicating that Egyptian blue emitted infrared rays. Although the Egyptian blue left on the cultural relics has been washed away or unrecognizable to the naked eye, this discovery has enabled scientists to find its traces in ancient cultural relics. Now, scientists also use Egyptian blue as a pigment for biomedical analysis and laser research.