Blue is a primary colour, alongside yellow and red, and can range from light blue, mid blue and turquoise to indigo, grey blue and dark blue. Blue symbolises tranquillity, safety and security.
The blue hour is the name for the phenomenon that the hour before sunrise in the morning and just after sundown in the evening takes on a blue colour under certain conditions. The blue hour is a part of twilight, but contrary to its description, it usually lasts only 15 minutes.
In urban settings, this time of the morning often creates a very distinctive atmosphere. The first lights come on, the first people hit the streets. The warm lights of the city contrast well with the blue surroundings.
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