Blue gives people the feeling that it is deep and can't see the edge. Just like describing the future, you can't see or touch it, but it makes you look forward to it. When it comes to blue, the concept of "sky" will naturally appear in people's subconscious. Some people will have the feeling of "universe" (deep blue). In some film and television dramas, when the protagonist is full of expectations, he will also smile at the sky and express his artistic conception full of expectations for the future. After a long time, this state will make people form a subconscious mind and make you feel that blue is the future.