Thank you for the example and screenshot, I've forwarded that upstream:
https://bugs.freedesktop.org/show_bug.cgi?id=7055
** Changed in: evince (Ubuntu)
Sourcepackagename: evince => poppler
Severity: Normal => Minor
Status: Needs Info => Confirmed
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PNG images in pdfs (black/white)
https://launchpad.net/bugs/46178