Do you currently use HTML formatting? Don't know or unsure? 'Tools' > 'Account Settings' > 'Composition & Addressing' for the mail account or 'Menu icon' > 'Options' > 'Account Settings' > 'Composition & Addressing' Select 'Compose messages in HTML format' click on 'OK' See second image below as an aid. If yes, then you should see the 'Formatting bar' in a 'Write' window. If you cannot see it, maybe it needs to be enabled: View > Toolbars > Select 'Formatting Bar' see first image below. Anything set via the Formatting Bar will only be used in that email. For helpful info at this link: * http://en.flossmanuals.net/thunderbird/composing-messages/ There is also an addon which can be used to auto quote colours in eg: Replies. * https://addons.mozilla.org/en-us/thunderbird/addon/quote-colors/ download to desktop or downloads folder. How to install: In Thunderbird Tools > Addons or Menu icon > addons click on gear wheel icon and select 'Install addon from file' see third image below. Locate the file you just downloaded and click on 'Open'. You may need to restart Thunderbird.