Spice up your email with colours; make it big and bold or small and italic, or whatever else takes your fancy.
To show the formatting tools, click the Make rich text link on the compose screen. A row of icons will appear at the top of your message to allow you to add formatting. If you're not sure what one of the buttons does, hover over it with your mouse for a tooltip.
If you usually use the formatting tools, you can change your settings so they appear by default for new messages:
You can configure the default style for how your text should appear in new rich text messages: