when colour correcting an image i find it very useful to have access to the underlying pixel values so that i can adjust precisely the values in the image that i am targeting, and also to be able to see the result of my adjustments in a numerical way (i can trust the numbers better than i can trust my eyes).

gimp and photoshop both have something like this. when i have the curves dialogue open, in gimp if i ctrl-click on the image it places a node in each channel of the curves dialogue for that value in the image. photoshop does the same thing if i shift+ctrl-click. after that i can very accurately adjust for those values.

photoshop also has an info docker that shows the pixel values under the mouse at all times, as well as under point references that i can drop onto the page with a shift-click. those point references are very valuable to me because they show the before and after values in real time at a static point in the image.

there are two other incidental features that i would also find great for my colour curves workflow -- the way photoshop and gimp allow for a histogram to be underlayed onto the curves dialogue, and the keyboard shortcuts (photoshop) ctrl+2,3,4,5 for the channels. but the info overlay is much more important to me.

here is an image of how photoshop displays this information:

https://ibb.co/mQxrW8

in the image the blue notes show information relating to the point reference that is on white part of the jet body, and the green references the point (not shown, but also near the point reference on the jet body) where i shift+ctrl-clicked on the image with the curves dialogue open.