If you move the center of one of the three color circles, then in R, G or B always only negative values are created. So, if I move in the direction of e.g. G, then the two remaining colors, i.e. R and B will show negative percentages, but G will always remain at 0.0%. When I do this, the image gets darker and darker unless I increase the brightness with the slider, to the right of it.
Is that normal? Wouldn’t it be more logical if the value increases in which direction I move the point?
Could it be that it is intentional? Moving the center point darkens the image.
But if you do not move the point with the mouse, but change the numerical value of a color with the mouse wheel or the small triangles, the brightness of the image remains constant.
I do not know what the intended behavior for the Color Grading filter is. However, I can say that its current behavior is very useful for my purposes.
Suppose I have a picture of a sunset. Suppose I want to shift the highlights to red/orange to emphasize the color. If the color wheel created positive adjustments, it would be very easy for the red channel to clip without me realizing it unless I kept a constant eye on the RGB parade scope. This would be tedious. A luma histogram or waveform alone would not be informative enough to tell me that only the red channel was clipping, as those scopes combine all three channels to get a composite luma value. Low blue and green values would mask any clipped reds.
Granted, a counter-point to my point is that I would still need the RGB parade to avoid clipping if I used the tone slider to raise the image back to its original brightness. I guess the main advantage of the way the wheels work now is that they will not cause clipping by themselves, which means I only have to tackle one problem at a time. If the wheels went positive, I would have to tackle color and clipping problems at the same time from the same control.
What a clear and convincing answer! Thank you, @Austin.
Yes, even if it seemed illogical at first, now I realize that it makes a lot of sense to reduce the counter colors instead of increasing the desired one. That way you don’t have to worry about clipping. Great.