Are you talking about new messages you are creating or reading of received messages ?

If you are looking to set up a default for all new messages you write: MAC: 'Thunderbird' > 'Preferences' > 'Display' > 'Formatting' tab click on 'Colours' You can set the default text colour and background colour. click on the coloured square, choose colour, click on OK

'Override the colours specified by the content with my selections:' Generally choose 'Only with High contrast themes' or 'Never'. If you choose 'Always' then you find it will also effect messages you receive and read.

The information in previous comment will change the background colour as it appears to you, but it is not hardcoded into the email, so your recipient who may have different eyesight requirements can choose to view the email as they prefer.

Thanks so much, that solved the problem.

To set a default background on emails and it is hardcoded into the HTML.

Set up a default for all new messages you write: MAC: 'Thunderbird' > 'Preferences' > 'Composition' > 'General' tab uncheck 'Use Reader's default colours' Then select the Text colour and background colour by clicking on the square colour icons and choosing a colour. click on OK

Advise caution as this will get hardcoded into email, so recipient gets same colour. Whilst the email may look ok to you, you should not assume others can read it with ease.

These don't help W10 users. How can I change the message page background color default? I.e. I have to change background for every message, default not working.

IrvW said

These don't help W10 users. How can I change the message page background color default? I.e. I have to change background for every message, default not working.

The instructions given above work in Windows, but the location is Tools/Options/Composition/General/HTML. Press Alt if the Menu Bar with Tools is hidden.

Got it, thanks.

Toad-Hall said

Are you talking about new messages you are creating or reading of received messages ?

In my case it is just reading the messages, plus the Options screens. I could neither read my messages in the message pane, nor read the message in a new tab after double clicking the message. When I went to Options, I faced the same devastating problem, and was therefore unable to make any changes.

You really shouldn't make background changes by default...reason?...because background and font colour changes are potentially devastating for low vision users. I'm so glad I found this solution, because without it, I'd have been well and truly stuffed. Email is such a fundamental part of our lives that if you render me unable to view my messages, it's like cutting the electricity or water...it's that crucial, especially to visually impaired people. You therefore have a duty to be a lot more mindful of how things look...and leave it to the user to make such fundamental changes.

The biggest problem you caused by making that change to the default colour theme, is that you a) overrode my chosen Theme, 'Dark', and b) the same change affected the 'Options' screens, so I was unable to see what I was doing in order to make the necessary change.