The lesson learned here is clearly for me. When I shot a documentary last September I was new to the 5Dm2 and didn't pay attention to color balancing (i.e. white balancing) the picture until I got into post production. The obvious result was that skin tones were all over the place when going through color correction. My main subject was a very dark skinned individual and his skin color went from red and saturated-looking to dull and green looking within a couple shots. This, while he was crouching in approximately the same place with the same lighting; the difference being the response of the auto white balance, given the scene. OK, fine. I has pre-planned to fix this during color correction in order to shoot fast. An example of the color shift is below...
After futzing with the color for much too long I decided that once again my dumb decision, "we'll fix it in post," wasn't the right solution. So...how? I had previously bought a Gretag Macbeth (now x-rite) white balance card for video work, but I was hesitant to take it on the plane to Seattle because it could get folded, bent, torn...etc. It's an expensive little piece of cardboard. That was a stupid apprehension.
Below are three versions of the same photo of the white balance card against an oak table. The first photo was taken with auto white balance. The second photo used daylight white balance (because it was about 1pm when I took the photo). The third photo used the custom white balance feature of the 5Dm2. The custom feature requires that you have either a white balance card or an 18% gray balance card (normally used for exposure metering). You then take a picture of the card near your photo subject and choose the photo as your white balance reference in a menu.
We aren't going for color authenticity here. That's different. We're really going for consistent color from shot to shot. Color correction then allows you to shift the color in post however you like without having to custom tune each individual shot. Something I should have thought about.
Below is a crop of the white part of the white balance card in each of the three above photos. Which is colorimetrically correct? Judging by my eye sight, the auto white balance looks closest to the oak given the light coming in from the windows at the moment. Which would I rather use and color correct later? ...The custom white balance of course. Lesson over and learned.
So what are other options? You could use a color temperature meter like the Sekonic C-500, but that costs $1k. DP's use these devices in professional film making for speed or where you're actually shooting on film. Cool device. Wish I had an excuse to buy it. The ghetto-fabulous option is to just use a white piece of paper...however, white paper typically isn't really white. It has it's own reflectance characteristics that can cause white balance to shift from shot to shot if the lighting changes (i.e. shooting over a period of hours with ambient). What you really want is a white balancing target with a broad smooth response across the visible spectrum. The paper option works well enough in some cases, not in all.