How to Change the Gmail Default Text Settings
With the Gmail default text options, you can get your message across. When you want your communications to include a bit more pizzazz, change the text options to something that better reflects your personality. Do it for an individual message or change the defaults, so Gmail uses your preferences every time. Use the Gmail General settings to change the default text Gmail uses when you compose email messages. When you change the settings, you choose the typeface, size, and color of the text. After you save your changes, every email you send uses those styles unless you change them again.
Use Formatting Bar Options
After you set your preferences as the new default, you can still modify the way text appears in an individual email message by using the formatting bar at the bottom of the email composition screen. No matter how you set the defaults, everything is editable in the window where you send an email. This is true whether it’s a new message or a reply or forward.