These numbers are used to understand, for example, how flash effects your images, and may influence your white balance settings. The color of the light emitted by a flash is rated at 5500? by many manufacturers; it is designed to imitate noon daylight (#3). If the flash produces light that is 5800? Kelvin, it has a slight bluish tinge. If it is rated at 5200?, it is slightly warmer, or more yellowish, than white light.
Since film is not relevant to most of us now, a setting of 5500? Kelvin as the white balance in digital cameras is just like using daylight film. This means that if you shoot indoors with tungsten lights, the pictures will have that yellowish cast just like the interior of the Vienna opera house (#4). I purposely used a daylight white balance to make the scene golden. If I had used 3200? Kelvin for the white balance, the tungsten lights would be reproduced with the correct color balance (#5). Different cameras indicate this white balance in different ways. Some will have an indoors setting while others will show a light bulb icon. More sophisticated camera bodies allow you to dial in 3200? K. These all mean the same thing—that you can expect proper colors when shooting under tungsten lights.
During the middle of the day when cloud cover has obscured the sun, the minute water droplets of the clouds absorb a certain percentage of the red and yellow wavelengths of light. The colder end of the spectrum, the bluish wavelengths, pass through unimpeded. As a result, landscapes and outdoor portraits will have a slight bluish cast even during midday. This also happens in thick fog (#6). In deep overcast, the blue color becomes more pronounced as it did in (#7). This is a tree stump that had been buried by a glacier for thousands of years, and in dark conditions under a thick cloud cover it went an intense blue/cyan when using a daylight film (this was taken in the 90s). If the cool tonality is unappealing to you, set the white balance to cloudy. However, if you like blue tonality in your shots, by photographing at dawn or twilight, the color can get quite intense. I photographed a foggy forest in Italy at 6 o'clock in the morning (#8) on a daylight white balance. Look how blue it is.
In digital photography you can tweak the color temperature in Photoshop to a certain degree, but it's much easier to work on color temperature issues in Adobe Camera Raw or Lightroom because you have so much control. That's one reason why it's so important to shoot in Raw mode.