In 2007 when I got my Digital SLR I took the free classes offered by National Camera where I got it. I learned many fine things. Maybe not as much as the people who hadn't read their manual before they got there, or the people who hadn't had any structured camera instruction. One of the coolest things I learned was a strictly digital related skill White Balance. First off what is white balance? Wikipedia has a lot to say
here But for those who don't want to go read all that, as I understand it digital camera takes a bunch of optical data and collects it on a sensor. If you're not shooting in RAW mode and editing your pictures in Photoshop or some tool like that, you're shooting in JPEG mode and it has to set values for the data. To set those values it makes some assumptions about what the world looks like, that there should be so much dark, so much light. Essentially that the world is a uniform 18% grey color.
Most cameras, even little pocket ones have a few stock settings, AWB or Auto, Florescent, Daylight, Shade, Cloudy, Tungsten, Flash, and Custom. AWB or Auto is where most default to, and many people never change it. It does a fair job. The others are mostly related to the sorts of light you are under. Florescent fixes the green skin tones that appear in pictures of very fair people in office and the like.
Custom is really the way to go if you have the few seconds to do it. It's easy. You do need something that is that mysterious 18% grey, or well any uniform light or medium grey, will work. I have used the inside liner of my camera bag. I have a
lens cloth that happens to be an ok grey card. Serious photographers will tell you that a
card is better, but this fits in my pocket and works ok. Cards are allegedly be better because of more uniform flat reflective surface. A sheet of paper will also work but might end up with slightly overexposed pictures.

So how do I use this? Well first I notice that Auto is failing me. See the golden hue of my living room. It's not realy this orangey golden. Also frequently it's tidier than this, but that isn't really relevent to the issue at hand.

Then I get out my grey cloth and I take a picture of it. It should be flat not all wrinkly but it doesn't seem to matter a ton in indoor light. You will notice this doesn't look too grey either, it's sort of a goldeny weird grey caused by the lights in my basement. Now the steps here vary but on my Canon Rebel XT I open up the White Balance settings. I then change to Custom. Then I go back up to the menu and choose the Custom WB option and it then shows me images, starting with the most recent one taken and gives me an option to select an image to white balance against. So I pick that one of my grey cloth.

Then I take the same picture again. Notice the more natural coloration. One last thought be sure and check your white balance as soon as you start taking pictures, especially if you use a custom white balances. Because the white balance you shot in your basement, or in your lightbox, or at the park, may be radically wrong in the other locations, but it will keep trying to use the last one you set.
Maybe tomorrow I'll do some white balance photos, in the great outdoors with all the snow. It's stunning what a difference it makes.