Using the HTML Editor:
Using message templates as an example, when editing your templates you will see this tool bar at the top of the text editor:
The second icon from the right, , allows you to edit the message's HTML source. When you click this button the template you will see the following:
In the HTML editor you have the ability to input inline HTML styles to format things like fonts, font color, size, etc. As you can see from the template shown above, a number of inline styles have been applied in order to utilize different fonts, colours, formatting, and images. For more information about inline styles, we have found w3schools.com to be a fantastic resource.