The color temperature of light is one of the most useful tools in a photographers bag. A few simple and useful examples of changing color temperature through a day are the difference between daylight, sunset, and night. Typically daylight is "White Light" Sunset is "Reddish Light" and night is "Bluish Light".
However what appears to our eyes is much closer to white light even when at sunset or at night. We do see the reds and blues but our brains shift them closer to white than reality. Essentially we see what our brains expect us to see.
What a photographer must understand is that the camera does not interpret light like our brains. The camera sees light strictly by its frequency. Understanding the temperature of light can open a whole new set of photographic opportunities.
Just after dusk when the reds have left the sky and yet the sky still has some residual light is called the Blue Hour by photographers. Here is an example of a Blue Hour photo of Yosemite Valley. If you look closely you can see a couple of the first visible stars of the night.
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