In the built-in Mail app on macOS, changing the background color of an email is simple, but not so obvious. You have to know where to look. It’s in the Format > Fonts menu when you’re composing an email. Remember the keyboard shortcut Command+T to get there quickly.

Here's how to set the background color of a message you're composing in macOS Mail.

Open a new message in Mail by clicking the Compose New Message button.

Select Show Fonts under Formatting in the menu bar.