It's generally better to set your camera either to an appropriate white balance setting (other than auto white balance) or better yet, set a custom white balance, keeping in mind, if your lighting conditions change for any reason, you'll need to create another custom white balance. In creating your custom white balance, there are several different ways of doing it. The simplest is to keep either a white card or a gray card (giving your camera an 18% gray reference point works just as well as giving it a pure white reference point) in your camera bag. There are some more sophisticated choices on the market though if critical color is important to you.
Upstrap, a camera strap maker, also offers an 18% gray microfiber cleaning cloth that can be clipped to a camera bag. The cloth (see image gallery) can be used to clean lenses and also serve as a gray card when needed.