Colour-code emails in Mail on Mac
You can make email messages easier to spot by using a rule to automatically colour-code them. For example, messages with a high priority could have a red background.
In the Mail app on your Mac, choose Mail > Preferences, then click Rules.
Click Add Rule.
Choose whether any or all of the conditions have to be met.
Click the conditions pop-up menu to set the conditions for colour-coding. For example, choose “Priority is high.”
Click the “Perform the following actions” pop-up menus, choose “Set Colour of Message,” then choose either “of background” or “of text.”
Choose a colour from the pop-up menu, or choose Other and use the Colours window to select a colour.
To colour-code messages manually, select the messages in the message list, choose Format > Show Colours, then select a colour. Mail changes the background colour of the selected messages in the list.
The colour-coding is visible only on your Mac; it’s not shown when you look at your messages on your other devices.