I noticed something which I helped color correct today and later viewed the material in a darkened room.

Your eyes will slowly adjust its white balance to whatever the current lighting situation is. You generally do not notice this, because it would be a waste of your attention. But you can easily check for yourself by looking out a window and asking yourself how white something is as time passes.

When watching video, your eyes will slowly do this too. If you're using warm/cool cards, the warm/cool effect will eventually be nullified since your eyes will just white balance to the warm/cool tone.

When you go back to proper white balance, then it will pick up a slight color cast of the opposite warm/cool. It looks like you've introduced a color cast when you didn't really mean to.

2- Whether or not your eyes will color balance to the display depends on a number of factors.
Your eyes have a tendency to white balance to the brightest point in an area. If the display is backlit by strong light (i.e. sun light), it is unlikely your eyes will white balance completely. In a darkened environment, your eyes are likely to white balance.
Angle of the bright light source to your eye matters.
The area surrounding the display. A bright surround will make white balance less complete(?). Gradients around the surround and the amount of articulation may make a difference.
Color temperature of the display may make a difference.

3- I would think that some of your audience will not get the white balance adaptation happening and see the warm/cool effect as one would like. Mild white balance adaptation may weaken it a little bit though..?

Hmmm.......ok..... but I still love my Warm Cards ®

How long would you have to look at this before your eyes adjusted to the color cast?

http://xs53.xs.to/pics/05443/screenshot.jpg

I could look at it all day and still call it warm.

I have never used the commercial cards. I used to use the Rosco gel sampler and hold up a very light blue or orange (or whatever) gel in front of the lens and point at something white. Same idea. As to the original comment, I do think that while your brain compensates to arrive at an internal white balance, Glenn's need to darken the room in order to "force" his brain to readjust his internal WB on the video picture underscores the need to pay close attention to WB, either for accuracy or effect, while on production. Because almost every viewer will have other visuals to internally WB to besides the picture on the monitor.

Emre:

White balance adaptation happens in some cases and not others.

Situation A:
If you are watching the footage on a display (filling the entire screen) in a dark room, then it is likely white balance adaptation will occur.
This has been proven and you can prove it to yourself doing something like:
Hook an external monitor to your editing system.
Apply the color corrector filter, and keyframe slow changes in the highlight white balance.
Turn the lights off, and all your computer monitors.
Play the footage on the external monitor. You probably won't notice any change. You may be able to hit the JKL keys to vary the rate of white balance shift.... if it's fast enough, you can see it.

Situation B:
You are watching the footage on a display where there's lots of reference white. The JPG is a very good example, as there is lots of reference white on people's screens. Your eye's white balance would likely "anchor" itself to the reference white and not the darker orangey-white in the video image.

Glenn: That is precisely the reason why professional color graders work in a neutral environment with controlled lighting. I should set my desktop wallpaper to medium gray, but I am too lazy...

Well, OK, Glenn, fine sounding theory. But so what?

JAG was all shot with a golden look, so were all the desert scenes for Sahara, it worked. In those cases, done with a lens filter rather than cheating WB, but still it works. This sort of warm/cool look is used in films all the time through selection of film stocks and use of filters, it establishes the look of a particular scene or show.

Nothin' wrong with the concept and I wouldn't label it a "fallacy."

I suppose it depends on whether or not there's the presence of not-so-warm/cool white in the image.

If you shoot on film, the natural s-shaped gamma curves will desaturate the whites in the image so it'd pick up less warm/cool color. Your eye would white balance to that, and so you still get the effect.
In you shoot on video, there is probably something in the shot that is overexposed and blowing out (if there is any shiny object, there will be a speculat reflection that is very bright most likely). This provides some reference white for your eye to WB to.

Perhaps the place where it really does happen is when you alter white balance in post... which is how I tested and saw this effect. So maybe warm/cool cards aren't such a bad idea after all.


Emre:
Looking over your picture again, in many real-world viewing situations I think it would still appear pretty orange. Your eyes usually won't white balance to highly "saturated" colors... i.e. street lights, household incandescents (about 2800K), magic/golden hour (well at least where I live, the sun reflecting off a car looks yellow).

Hmm... so are you saying that white-balancing a camera before a shoot is not necessary because the viewer's eyes will do it for us?

You should still white balance because the viewer will notice sudden jumps in white balance.

It's just that if you use warm/cool cards, you may get an un-intuitive effect where the color cast disappears and then you see the opposite color cast when it cuts back to normal WB.