Invert brightness but not color

[AnotherNeko]

I want to add an option to invert the brightness but not the hue of every color on the webpage.
I'd happily help by contributing an algorithm (pseudo-code or JavaScript or C++) that takes a color input RGB(A) and performs the correct color transformation to keep the color but get the opposite brightness, returning some different RGB(A) with the same dominant color as the input.

[doodhout]

That sounds simple enough: convert from RGB to HSL (hue-saturation-luminance) and only invert luminance while keeping the original values for saturation and hue.

[AnotherNeko]

I created a branch with hue invert, but it will always invert the hue. Once this branch has a fully functional invert hue checkbox, we can submit a pull request.

[Max-Github]

I do not see any issues with adding this feature to the main branch.

Thank you for your contribution.