Manual white-balance for non-neutral lighting When you put an 18% gray card under, for example, an incandescent light, it's not supposed to look neutral gray. It's supposed to look orangish-gray, like your eyes see it (because it's reflecting some of the orangish light from the lamp). In such an environment, if you set manual white balance in-camera using that card, then the card will be captured as neutral gray, but the rest of the scene will have a much cooler tone than in real life.
Assuming you can't make significant white balance changes in post-production (e.g. because you're recording 8-bit, not raw) and you want to preserve the effects of the scene's lighting in the captured image, what is the correct strategy?
Should you just estimate the color temperature manually? Treat the gray card as neutral and hope you can fix everything in post?
I think your eyes acclimatise to the ambient colour temperature in the room, so one tends not to notice that whites are looking warmer under incandescent light, unless there is a cooler light source nearby to compare it with.
If you don't plan to do any colour correction in post, then you should shoot as close as you can to your desired output. But this is difficult to achieve because of the acclimatisation I mentioned in the previous paragraph.
This is why people shoot to a neutral standard of white that can be defined using their camera's metering.
In general I have would say that there is no neutral lighting - all light has a temperature, whether cloudy outdoors, fluorescents, incandescents etc.
What is more important is to avoid mixing different light sources on the same subject, because it then becomes very difficult to make any corrections without everything else looking wrong.
Small amounts of colour correction from 8 bit material can be done without the image falling to pieces (although it's not ideal). The bigger problem with 8 bit video is when you try to raise shadows or recover highlights.