One of the technical features that I like most about digital cameras is the ability they give you to match the sensor's color response to the color of the existing light using the white balance control. In the old (i.e. film) days, if you wanted to match a film to the light source you either had to choose a film that was balanced for that type of lighting (daylight film for daylight, tungsten film for tungsten, etc.) or use filters to "correct" the film for the existing light. With digital cameras, of course, you just open up a menu and tell it what the predominant light source is and shoot--and you can even fine-tune the response via a color-picker/color-temperature chart on with most DSLR cameras.
But you don't always have to choose the correct white balance. In fact, sometimes you get a more pleasing or more creative photo if you intentionally use the wrong white balance. If you use the tungsten setting in a daylight scene (as I did for the shot above), for example, you end up with a photo this unnaturally blue. Why? Because in order to balance the sensor's response to tungsten light, which is naturally very red because it has a warmer color temperature than, say, daylight, it adds additional blue to the scene. But if you use that extra blue in daylight scenes, you end up with photos that have a very cool twilight appearance. That is exactly what I did to get the shot of the Christmas tree on my front lawn. I did shoot the photo at twilight and there is some artificial lighting (LED) but the predominant light is just daylight. I exaggerated its blue color by choosing a tungsten white balance--which, in effect, put a blue filter over the image.
You can do the opposite, too (and I often do). If you are shooting on a very cloudy day where the daylight has a lot of blue in it, you can use a "cloudy day" white balance setting to add warmth to a scene--that's what that setting is for. But you can also use the cloudy day setting (again, it's designed to add warmth) on a bright sunny day and that in turn will add extra warmth to portraits, landscapes, etc. In fact, I almost always use the cloudy-day setting--it is almost my default white balance setting for outdoor scenes because I like them warm.
Of course, the simplest way to tweak the white balance in all of your shots is to shoot in RAW and then adjust the white balance after the fact. The Adobe RAW converter, for example, has a white balance slider that essentially lets you make your white balance choices after the shot was made.
By the way, here's an interesting side note on this shot. When I was taking it, I noticed that the lights seemed somewhat out-of-focus compared to earlier shots I had made of the tree at night. I had to ponder it for a few minutes, but then realized that what was happening was that, because there was still some daylight in the scene, I was seeing the clear plastic tube that encases the lights. At night the lights seem much more precisely focused because that clear tubing basically disappears. All that you see at night are the colored lights. Interesting!