Created attachment 147581 [details] the setting discussed here Within the discussion (https://invent.kde.org/graphics/okular/-/merge_requests/587#) of my previous bug report (https://bugs.kde.org/show_bug.cgi?id=451573) I was convinced that I was wrong, but the same line of argument that has convinced me imposes a further clarification. Those settings are not about foreground and background, nor about text or images. Any text or image would be treated as a monochrome one (with degrees of black and white), "Dark color" setting will replace black, "Light color" setting will replace white. For example, if "Dark color" is set to red and "Light color" is set to purple, the proportion of red and purple will follow the initial proportions of black and white from the monochrome base. That means that "black" should be used for "dark" and "white" for "light" as more adequate naming of those settings, because that's what is happening in fact: the color selected under "light color" setting (purple in example) will 100% replace light color only if that is fully white, otherwise (if it has some degree of black) it will mix it with the color set under the "dark color" setting (red in example)! The advantage of that would be to add more clarity: dark and light are relative terms, black and white correspond exactly to what is happening here.
The setting discussed here imposes degrees of just 2 colors on a dark/light structure — and this structure can only by a monochrome one, with degrees of black and white. The 2 colors that can be selected here are proportionally replacing black and white within the monochrome structure. When we set a color (e.g. red, #aa0000) under "dark color" option, #aa0000 will effectively replace absolute black (#000000), and if we set it under "light color" it will replace full white (#ffffff).
I mean that the name of the option 'Color mode: Change dark and light colors' should NOT be changed, because it describes well *what* it does, but that the 2 color selection options (which describe *how* it does it) should be renamed to "black" and "white".
In the present form, a real color (expressed in numerical form of complete clarity) is supposed to replace something called "dark" or "light color", which is not a real color but a relation between two colors, and thus cannot be replaced by a real color. (What that specific, numerically defined, real color replaces is pure black or pure white).