Option request.

[Cabral]

To select the size and color of the font.

[benw]

You mean when composing messages or as a default how all the messages appear?

When composing if you click HTML at the bottom right, a formatting toolbar will appear at the top of the textbox. If you mean a the default font, you can edit the file:

skins/default/common.css

All the font size and type options are in there. Make a backup copy first.