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I'm late to the party and I'm not going to directly answer your question - but I'm hopeful that some of this might be a bit useful.
Regarding color balance for scenes that are intensely colorful and especially in which the light's color and/or the overall color of the subject is very strong in one channel, using jpg and a in-camera color setting is not the best approach. The camera is going to attempt to essentially move the overall color average of the scene towards neutral, and this creates problems when the scene is actually far from neutral. Given the variables in the light itself and in how you might interpret it, here it is almost always generally better to shoot in raw and save the decision making for the post-production phase where you have the most control and still have full image data in the raw file.
Determining the "right" color balance is different than determining the "accurate" color balance, and even the latter leaves you with at least two choices.
If you are going for supposedly accurate reproduction - which I do not generally recommend except in a few limited circumstances - you could either go the gray card route and attempt to render something that is known to be gray as an equivalent gray tone or you could presume that your camera's raw mode renders an "accurate" version of the coloration that was there.
There are problems with both of these, and often the best results is somewhere between the two.
The problem with the gray card is that it essentially eliminates the interesting colorations that probably made the scene interesting in the first place! If you shoot in warm "golden hour" light and then shift everything so that your gray card is gray... you just eliminated that lovely, warm light coloration that drew you to photograph the scene in the first place. Yes, you'll have neutral colors - white will be white and gray will be gray and, hopefully, other colors will come along for the right - but it will look like you shot in neutral light rather than warm light.
The problem with going with the "accurate" rendition of raw mode is one that we're all familiar with if we have shot subjects, say, in shadow and illuminated by open sky. In the actual presence of such a thing, the scene looks fine to us - but when we look at the resulting photograph the coloration from the sky or other sources seems overdone and grotesque. (Anyone who has shot snow in shadow is familiar with the actual sky-blue color of snow!) On the scene, our visual system compensates and reassures us that blue snow is actually white, but in a photograph this breaks down.
The "best" outcome is perhaps somewhere between these two extremes. You don't want to neutralize the natural coloration of the light that gave the scene its character, but you also don't usually want blue snow. So, as with some many things in life, the answer is some sort of subjective compromise between the two extremes. In many cases I want to move the color balance away from the supposedly accurate tones of the raw file, but not all the way to the neutralized coloration of the gray card version.
How to get there? There are many techniques that can work, and assessing which one is right is a personal and subjective matter. I have seen people use the gray eyedropper tool in a curves layer and click around the image until finding something that seems like it should be gray. I've been known to add an "average" layer in photoshop, click on that with the gray eyedropper, delete the gray layer, and then adjust the layer opacity to taste. In essence, what one frequently does is move the balance from the raw color toward but not too the gray card value, making careful (and experienced) but subjective judgments about how much is just right. Two photographers will come to different conclusions.
Sorry for the longish answer, but it isn't really a simple issue and it is not susceptible to an automated methodology.
Quick question for the group on what result you would expect to see using the following lighting scenario and WB setting method (custom).
Say you took a photo of a proper gray card under weird lighting such as golden hour on the field, or unicolor stage lighting. In that specific lighting, you then on the Canon Camera set the White Balance (WB) to use that customer setting of the gray card shot you just took.
Now, say under that same lighting (call it pink), if you took a jpeg photo of a pure white sheet of paper and displayed it...Show more →