This article includes the full text of Tip #4 of my book, Pet Photography 101 (page 14) plus some additional information and tips.
Color temperature is an important consideration in photography. By learning what types of light have what approximate color temperature, you can more easily choose a color temperature and balance your lighting. For example, daylight at about noon in New York City in the summer is approximately 5500ºK (Kelvin), and most traditional lightbulbs and gallery halogen spotlights are about 3500K. If you were to photograph a scene under those two lighting conditions, you would generally choose the daylight color temperature setting for the 5500ºK light and the tungsten color temperature setting for the 3500ºK light. When you do that (in a perfect world), all the neutral colors (grays) in your photo will be reproduced as neutral.
Alternatively, you can use a gray or white card of some type to make a custom white balance, as long as your camera has the capability. There are many gray cards on the market, from very small ones that are integrated into lens caps, to large black, white, and medium gray cards that are also collapsible reflectors [see w1.13]. Here’s a quick tip: If you don’t use a custom white balance, set your camera to the “cloudy” white balance setting (look for the cloud icon) when shooting outdoors. It is an excellent starting point that will give most of your outdoor photos (or window light photos) a slightly warm tone, which is great for photographing pets and people. Additional links to articles on color temperature and filters can be found here [see w1.15].
For more control over your photos, turn off auto white balance. Auto white balance can cause your camera to shift colors wildly from shot to shot. It’s better instead to choose one color temperature similar to the color temperature of the light in the room, or to make a custom white balance as described above. If you photograph a gray card in one photo, you can then use it later to batch adjust many photos as long as they were shot under light with the same color temperature. You can then “gray balance” and batch adjust the images in an application like Adobe Photoshop Elements, Adobe Lightroom, Apple Aperture or Adobe Camera Raw. A selection of gray cards can be found on this page on Amazon.com. A unique product to consider for gray balancing is the ColorVision SpyderCube. It is not flat, so you capture light from different angles. It also includes a “black trap” area for capturing shadow values which is ingenious.
You can also use color temperature creatively by choosing a color temperature setting that’s different from the actual lighting in the scene. For example, if you set your camera’s white balance to daylight white balance mode and photograph the inside of a home lit by standard light bulbs, the overall color of the room will be very warm, which you may like a lot. This is because the camera is expecting daylight-balanced, 5500ºK lighting, but you are giving it a warmer light. Also, if you use software that can read and process Raw files, you can change the color temperature of Raw files with less loss of image quality compared with JPEG files. Most studio and on-camera flash units have a color temperature of about 5500ºK, which is important to know when you are balancing flash with indoor or outdoor light. Plastic or glass filters can be used over the flash to match the indoor light if you want to balance the color temperature.
To help understand color temperature better, the chart on this page shows at what color temp a neutral gray would be neutral if the color balance is set to Indoor (or Tungsten-3200ºK) or Outdoor (5500ºK).