To be fair this is different for an email application because most email content assumes a white on black. This means that if you want to display the content in

To be fair this is different for an email application because most email content assumes a white on black. This means that if you want to display the content in black on white it requires non-trivial and heuristic based fiddling. Thunderbird has always followed my Linux GTK theme so I don't really know what you are complaining about.