Next time someone tells you it's a black and white issue, ask them what colour temperature they mean.

You see, light slightly changes colour depending on its source.  Without getting too technical (I'll leave that to Wikipedia), an object seen under direct sunlight is of a slightly different colour than the same object seen under, say, a common household lightbulb (which will make it a little more reddish), or a fluorescent light (where it will be a little more greenish).

The human brain, however, is a marvel of adaptation.  Since we know what colour human skin is, for example, we don't 'see' the greenish tone that skin takes under typical office/classroom lighting.  Instead, it corrects for this automatically and we see people, not Martians.

A digital camera's sensor, on the other hand, doesn't work this way.  It records the scene exactly.  Film was the same; if you wanted to take a photo in an office that was light by fluorescents, you'd have to toss a magenta filter in front of your lens to correct for the greenish colour of the light source.  Nowadays, you can set your camera's white balance instead, correcting what the camera sees without the need for expensive, fragile filters.  These settings are typically listed as automatic, daylight, cloudy, tungsten, fluorescent, flash, and custom.  Pick the one that's closest to your current lighting situation, and you're good to go.

What's more, is that you can make photos more interesting and dramatic by simply setting the camera to a white balance that doesn't match the scene in front of you.  I took the three photos shown below one after the other, all at the same exposure value, but with slightly different white balances.

No processing of any kind was applied to these images; notice the change in saturation, especially in the blues?  That's entirely due to the white balance setting.  Try it and see what creative uses you can come up with!

This is what makes mixed-lighting scenes difficult to shoot.  Where do you set your white balance, such that colours look normal?  More on this in a future post.