Remapping only L in Oklab will be much more efficient than using the standard combination of invert() and hue-rotate(180deg), because it keeps hues correct while messing up saturations and making reds darker. With a and b remaining the same, any red highlights remain red. What about images and graphics? Remapping lightness in an image will make it seem like a negative image, hence you wouldn’t use image XObjects, but then diagrams that have white backgrounds end up as white boxes on a dark background.