The difficulty Gimp 2.10 has with histograms in the “curves” window is that they are shown as gray on a gray background with a gray grid. This crafty colour-scheme is designed to weed out those of us with less than perfect eyesight.
With the “dark” theme, the gray histogram in the “curves” window is slightly lighter than the background and slightly darker than the grid, which is drawn before the histogram. When we have highlight clipping, the grid on the right side is dark where the histogram has overwritten the grid.
By contrast, the histogram in the “levels” window is white, or at least much lighter than both background and grid, so it is easier to see.
The “light” theme shows the curves histogram slightly lighter than the grid, and we see in the screenshots from @ajax in this thread. We can see, but only by looking very carefully, that blue has clipped massively.
Other histograms shown above have histograms sensibly shown in colours. If a designer wants to make them less obtrusive, the colour could be blended 50% with the background gray.
[rant]I remember, around 1980, when computer screens didn’t have colour. We had different shades of gray, including black and white, and had to make do. Modern computers have colour screens but some designers hate to use colours and also hate both black and white, and especially hate the high contrast of black and white together. They adore having various different shades of gray things on gray backgrounds, with low contrast.
Microsoft Windows has a “high contrast” setting that sometimes writes black characters on a black background. Grrrrrrr.[/rant]