[KevinH]

It is not a bother, at all.

It is just a "feature" that I think will not benefit that many people, imho.

If I am using many colours in a epub's css, then it means the book is limited to light mode or dark mode, not typically both.

If meant to be read in light mode (ie. using dark borders) then Previewing it in light mode makes the most sense. The opposite is true for an epub that is meant to be read in dark mode.

If an epub is meant to be read under either/both, then the colours must be chosen to work in both modes.

And in none of those cases, would inverting colours be needed as Preview would be done in the mode it was designed for.

So in many ways, adding invert will just hide the fact that when choosing border colours, you are constraining under what mode the epub can be read in.

Sorry.