Ok @George , I will refine my wording:
If there is some white in the image AND it has a colour cast AND the image NEEDS white balancing then you can use the histogram to help you merge the RGB peaks for the white portion of the picture to properly white balance the whole image.
The flying lobsters picture has no white to colour balance so you have to do it by eye, not that this picture needs it.
NO!
The histogram is a global representation, you canāt use part of it.
From the internet. Show me your method.
And one with a wrong wb.
George
Speaking of the Internet - search Google for: āwhite balanceā ātone curvesā (use the quotes) and you will find articles where professionals describe how the tone curves tool can be used to correct white balance. No one is suggesting itās a panacea, George. As Keith said, you have to be prudent about when to do it and when not to. But there are times when it might be the best method available. Keith used it effectively in a real-world situation involving underwater photography. Isnāt that enough to share it as something useful?
@Egregius ,
Tone curves are used to correct colors. White balans does that too. But thereās a difference between them. However the result can be satisfactory.
But that is not what Iām opposing to. Itās the use of the histogram in combination with the desired result: a right wb. Thatās just impossible.
Read the opening post. Keith is trying to archive a right wb by trying to get overlapping shades of the 3 channels in the histogram. Heās creating a monochrome picture that way. The image he used is nearly monochrome, no extreme colors so in this case he might think he used a right way.
Doing so with the lobster is just impossible.
Keith wanted a white part in the image so I sought for a good example on the net. Tell me how to archive a good wb based on the histogram.
Iām not aware of any possibilty to show the histogram of a selected part of the image. The only way is the gray pipet.
George
If the goal is only to balance the āwhiteā portion of an image, that should be straightforward enough using the histogram and curves by using the tone picker in the white portion of the image you want to ābalanceā and aligning the histograms in each channel. But this does not necessarily equate to white balance, and it may create undesirable color casts in other parts of your image that will need to be addressed.
While this is a powerful and effective tool for color editing some images, as described by @KeithRJ, in most cases, this is simply not an accurate way to achieve white balance in any image, because there is a good change you wonāt achieve a single neutral pixel working this way.
Iāve spent quite a few hours with this hands on (not mathematically) in the last couple of weeks, and while I can find some esthetically acceptable results, I have not been able to achieve white balance using the histogram and curves. Far better for me to choose what I consider neutral in the image with the tone picker, or simply pick a preset like daylight, shade or cloudy as a starting point. @Joanna 's image is correct and does not need adjustment, because itās probably recorded at a daylight color balance in daylight conditions on a clear day. Underwater photography has a unique set of challenges compared to terrestrial photography, and creative use of the tools at hand may be necessary. But even @KeithRJ 's image can be acceptably balanced by picking a spot that should be neutral. It will have a color cast due to the color of the sand as he described, but that can be edited just as well from there. He may prefer the results he achieves using the histogram and curves from the outset, which completely validates that method for color editing.
In fact the histogram more-or-less does that. The histogram graphs the number (count) of all pixels at every brightness in the picture from black to white. If you want the adjust the brightness and or colours in the darker area of your image you adjust the left side of the curve. If you want to adjust the lighter areas then you adjust the right side of the curve.
A better tool is the Waveform / Parade tools found in some software and extensively used for video editing.
Going on to WB: For RAW files you have two sliders; Temperature which adjust the Blue and Yellow tones in the image; and the Tint slider which adjusts the Green and Magenta tones. For non-RAW you only have the Temperature slider (why DxO decided on this I have no idea because all other programs I have used have both sliders).
Now if you go to the Curves tool and and select the Blue channel and make an adjustment you will see the result is very similar to the Temp slider and the background of the Curve actually show Blue in the top left corner and Yellow in the bottom right corner (yellow is opposite of blue) and moving the curve towards these corners adjusts the image in a very similar way to the Temp slider.
Now select the Green curve and make an adjustment you will see Green in the top left corner and Magenta in the bottom right corner just like the Tint slider.
The Red Curve has Cyan as itās opposite colour.
So you can see that adjusting the Blue and Green curves is the same as adjusting the Temp and Tint sliders with the added benefit of being able to adjust different parts of the histogram separately thereby adjusting WB to different extents in the shadows and highlights.
Additionally you can also adjust the Red / Cyan tones of the image if you need to, just like I need to in my underwater photos.
Some additional background. I have been taking underwater photos for about 20 years now and started with simple cameras that could not take RAW images. I now use a camera that does take RAW.
I started editing with Lightroom and used the pipette mostly for WB but as the years progressed and I revisited these images I developed better methods to perform WB and have now settled on the Curves tool which works really quickly and easily for these photos and gives me better results.
This thread was intended to show members that there are other ways of editing photos. There is no right or wrong way and some comments have made me look at the details more and helped me better understand what is happening.
I do have to point out that this method works best on underwater photos taken without artificial light, but can be used where the tradition WB tools just donāt work well enough.
I hope this has helped readers look at other tools and find uses for them that they had not realised were there. We are all learning all the time and asking questions no matter how silly they may appear makes one questions things which triggers the learning process 
One question: wouldnāt the use of a gray card be an option? Before or immediately after a shot, it should allow a correct white balance and would be less time-consuming.
Yes it would but not practical when trying to photograph fish
@KeithRJ
I know what the histogram and tone curve and its sliders does. But you make a few wrong assumptions.
Iāve mentioned tis several times, this will be the last one.
I would like to see how you can adjust the colors on the last hand image using your method.
George
I donāt understand that. I had written after the shot. Your pictures show fish directly above the seabed, so you could put the card there. But this should not be made of paper. 
@George you canāt get to the first image by adjusting the Temp slider, not even close. As it happens you canāt with the curves either so I donāt know what was done to the second image to get it so bad!
And, WB is adjusting the colours so that the imageās colours are correct for the ambient light it was taken under. WB is not a special function that cannot be accomplished in other ways and with different tools.
WB using the tools provided only allow you to adjust Blue/Yellow and Green/Magenta which may not be enough to get the right WB.
Only after the photo is taken but you need to follow the fish as long as possible to get the best shot and the conditions (depth, light direction etc.) constantly changes! You just donāt have the time to use a grey card when photographing fish.
A right wb correction is not only done withe the color temp, also with the tint. Using the gray picker on the sand gives me 9545K and tint 108.
But what youāre doing is trying to get the shapes of the channels in the histogram covering each other. Youāre creating a monochrome,BW, image. As I wrote in my first post here. I just donāt understand why nobody sees that.
Iām still waiting for the result with the ladyās hand.
Wb is done through parameters used in the demosaicing process. That process includes also the gamma correction. Thatās why you wonāt see the color temperature in non raw images. And itās complete impossible for doing so. Just for the simple reason that the color temp doesnāt mean the color temp of the image, itās the color temp correction. I still think 5400K in PL means no correction. If my image is illuminated with a light source of 3000K then the correction will be letās say 7500K to archive an image temp of 5400K. Donāt hang me on the numbers. Thatās also the reason why the low color temp correction is showing blue and the high numbers is showing red. Just the opposite of what is.
George
First show me how you correctly WB this image with the Temp slider only!
I canāt. I would use the gray pipet as I did on your image in the beginning of this thread.
Now itās your turn. How would you correct wb in the last ladyās hand image using the tone curves?
George
You canāt WB this image with the tools available because it is not a valid image, full-stop. I believe it has been manipulated in such a way that it cannot be fixed! I canāt fix it and nor can you @George !
Take a photo with the wrong WB and send it to me. I donāt trust images from the web.
@KeithRJ ,
My main problem with your method is the use of the histogram. You may think you archived something like wb correction in your images but youāre creating BW images. With your images it was easy for they where rather BW. If your channels cover each other, have the same shape, then youāve a BW picture. Take any image with more colors and youāre in trouble. Thatās why I posted the lobsters. But you wanted some white in it, your images didnāt have that either.
The ladyās hand was a picture I found on the net, AI generated, but with a grey card. No good also.
George
George, look up what a āstraw man fallacyā is. Thereās no point arguing with you because you arenāt taking everything Keith or others have said about this into account.
He is not, because the pixels in the RGB histograms do not relate 1:1. Itās more true that the images he is editing are already very close to monochrome (and monotone) before editing. I will agree with you that what @KeithRJ does with curves and histograms does not lead to a white balanced image necessarily rather than an image he finds esthetically correct. And using the same method on images with more complex tonality and color is often not possible.
