I suggest pressing the shift key when you click 'reply' to switch you to plain text for this one message. I think that may eliminate the color issue.

I suggest pressing the shift key when you click 'reply' to switch you to plain text for this one message. I think that may eliminate the color issue.

Thank you for the suggestion. Yes, it eliminates the background colour. Unfortunately, it also eliminates all the HTML formatting of the included message which I am forwarding, or to which I am replying. In some cases this may be fine. In some cases, however, it ruins the included message.

I guess I should clarify my question: How can I change the background colour of my part of the reply or forwarded message which I am composing, without ruining the formatting of the included message? How can I override the background colour set by the sender in the original message, but not discard all HTML formatting?

Other than modifying the HTML (for which, you would need an addon), I suggest writing your reply, and then highlighting the reply, and selecting the background color option in compose menu and set to a different color. If you select a dark color, consider then changing your text to white. I agree, this is messy, and I wish people who send messages in color were sensitive to us, as receivers, who must struggle in our replies.

David: Thank you again for your attention.

I tried what you suggested: writing a reply, highlighting the reply text, and attempting to set the background colour. However, I do not see a "compose" menu in my copy of Thunderbird (115.10.1 (64-bit) on macOS Sonoma 14.7.1).

I do see a "Format" menu. It has a "Text Colour…" item and a "Page Colours and Background…" item. Neither was successful in changing the background of the top part of the reply message, which contains my text.