Message body background color should match window background color

[uniquePWD]

Checklist

• [X] I have used the search function to see if someone else has already submitted the same bug report.
• [X] I will describe the problem with as much detail as possible.

App version

6.901

Where did you get the app from?

Google Play

Android version

14

Device model

Pixel 8 Pro

Steps to reproduce

Look at an email in dark mode

Expected behavior

Email body should be the same as the header

Actual behavior

Email body is coloured

Logs

No response

[uniquePWD]

[cketti]

This is not limited to the dark theme. Currently, the message body background color also doesn't match the window background color when using the light theme.

[kewisch]

Let's handle this as part of #4198, I'll make a comment there.