Just realize that for a white balance reference, whiter is not always better.

Actually, good white balance cards are light neutral gray so that the white balancing is done closer to the middle of the camera’s sensitivity range, for more accurate results. And a properly made and maintained white balance card (e.g. don’t let it get bleached by the sun when not using it.) is more accurately neutral in color than a white shirt or piece of paper. It is common to have “white” t-shirts that are actually too yellow or even too blue (many fabric cleaners use bluing agents to make whites look whiter), even when they look plain white to the eye.

A surface that is too white could also give bad readings if it is overexposed during the white balance check and any of the color channels are clipped at the maximum sensor value. What’s worse, many camera models won’t give you any warning if this occurs when setting white balance… they’ll just use the bad data as if nothing is wrong. Shooting a white balance card as the first in an image of RAW images. then white balancing them later in a photo editor is usually better than using custom white balance in the camera and shooting JPGs. Just make sure to check that the image of the card is not overexposed on any color channel when you take the shot.

Of course, how picky need to be depends on what you are trying to achieve. A lot of photos do not actually need perfect white balance. Many times a warmer image actually looks better.

Kind of interesting, most of it is pretty common sense, but it was kinda cool to see the white t-shirt theory discussed somewhere else, just after I saw it here.