Thanks for the report, you found a real bug. That document is a scan processed with Adobe Paper Capture, which adds an invisible OCR text layer on top of the scanned image. Veil sees that text and treats the PDF as native, so it protects the image from inversion instead of inverting it. The dark border you see is the PDF background margin between the page edge and where the raster image starts, that margin gets inverted by the CSS. I'll probably need to cross the text detection with image coverage, meaning that if there's an image covering almost the entire page, it's a scan even if it has native text. Thanks for the specific document, it'll be very useful for reproducing the issue.