Few changes can as dramatically affect the feel of an image as those to color. One moment a straight-faced person is content in a golden glow, the next that same expression tells a different story when the tones are set to blue.
There aren't many elements of photography to be passionate about, though two that rule almost all else are light and color. There are striking similarities between the two, insofar as how they can set scenes and set the mood of a captured moment's story, but they're also intrinsically linked. A high-key image will seldom make sense if it's blue in tone, and conversely, low-key images with warm tones suffer a similar problem. That isn't to say there aren't plenty of real instances in which it's dingy and orange or bright and blue, but color theory and T.V and film's use of it dictate a certain way of looking at scenes, among others.
When you stray from the extremities of exposure, as most photographs, videos, and films usually do, you have tremendous control over how the scene is perceived, just from color theory. But that only speaks of the mood, and doesn't touch on just how much creative control colors in an image give us as photographers. Altering colors of your images can turn the bland to memorable and the nice to beautiful. Forgettable sunsets can be transformed into stunning with as little as a well-chosen gradient.