I use the dark theme, however I tried to switch to other themes.
The received email appears empty, but if I select all I can read it.
I can’t find the way to make the background dark or the writing black.
Note: Sometimes the email is displayed correctly, but most of the time is white over white.
I am attaching one screenshot before selecting and the other after selecting showing there is text, only it was invisible. 
Hello Eliezer,
We’re sorry for the inconvenience. Is this something that only happens in the dark theme? Or also in the other themes? Is this an issue with e-mails from a specific sender of with e-mails from different senders? When you say ‘sometimes the email is displayed correctly’, do you mean that you can sometimes read one particular e-mail and sometimes the same e-mail gets displayed in this way?
You could also check your settings in Menu ->Tools ->Settings -> Mail -> Read - Preferred Style
Thank you,
Maurice