[Evolution] Evolution dark theme + 'reply' imposes dark theme in message

[Michael Wenyon <michael wengam com>]

I am using Evolution 3.22.2 in Debian testing.

If I set Global Dark Theme 'on' in Tweak Tools, or if I set the GTK+
theme to Blackbird, then every time I 'reply' to a message with a white
body, Evolution changes it so it has a dark theme: dark background,
light text etc. 

I would not mind if that was just for my display, but the dark theme
gets applied permanently to the message so that the receiver also sees
it that way.

The behavior I expected is that I could work in a dark theme and my
correspondents would be unaware. It would be OK for me if 'reply'
created a draft with a white background, and I believe that Evolution
behaved that way for a short while, two versions ago or so.

In Composer Preferences, there is a setting that can be checked
'Inherit theme colors in HTML mode', but this does not seem to make any
difference either way to the behavior I am describing.