Strange it's only effecting Reply and not Write.

Changing the colours isn't obvious but there are two little boxes to click, see screenshot below.

What do you have for Settings/General/Language & Appearance, Colours (see picture)? You might have to change the override setting, and the OS colour settings could be interfering.

Strange it's only effecting Reply and not Write. Changing the colours isn't obvious but there are two little boxes to click, see screenshot below.

Finally found something that helped.

But it's strange that I selected white text on a black background but replies show in blue text on a white background. I found it here:

What do you have for Settings/General/Language & Appearance, Colours (see picture)? You might have to change the override setting, and the OS colour settings could be interfering.

Found it finally.