[Evolution] Foreground font color?

[Paul Smith <paul mad-scientist net>]

So, I'm using Ubuntu 20.04 but to get a newer version of Evolution I'm
using flatpak.  Just yesterday I installed the latest flatpak for
Evolution 3.44 and now I'm seeing something odd: I use dark mode on my
system and when HTML messages are shown in the message preview, the
background is dark but the text is still black which makes it almost
impossible to read.

I've checked and these are simple HTML messages with no font or color
specification in them.

With the previous version of Evolution, 3.42, the background would be
dark and the text would be light, in this situation.

Is this a bug, or is it somehow related to the "improved" dark mode in
the latest Gnome (which I don't have)?

Is there any way I can force it?