[DiapDealer]

Almost correct. But it's not that the foreground color request is not being respected, it's that there is no foreground color property to BE set for that particular Qt Widget

You'll find that there's very few diehard Sigil users who use Book View for proofing, and even fewer that use it for editing. I understand the desire to change the colors, but most people want to see how the epub is actually rendering. Custom colors and user styling being applied will muddy those waters.

A feature request for integrating a custom user stylesheet to override the epub's styling is not likely to be accepted. Overriding an epub's internal styling is more of an epub reader feature than it is an editor feature. Besides ... Book View is not really being actively developed any more. It's days are numbered.