[JimmXinu]

I was testing some of my own code using CSS body { background-color: #66ff66; ...} which is an obvious bright green background.

But the Calibre book reader doesn't show me that green.

I see it in the Calibre book Editor, and setting the cover from the epub also shows green--just not in the reader.

If I go into the reader's Color preferences, I can change the background, but it appears to ignore the "Override all book colors: Never" setting.

I'm seeing this on Win10 in Calibre v5.6 (portable) and v5.10.1 (64bit), with reader launched from Calibre GUI, from file extension association in the OS and from the Content Server.

Calibre v2.85.1 (portable) did show the green.

I did check for any existing threads or bug reports about this and didn't find any.

Minimal example epub is attached.