Click Page Layout tab | Fonts | Create New Theme Fonts.
For more on colors and themes, take a look at these articles:
Which Color When? (Part 1)
http://blogs.msdn.com/b/jensenh/arch...10/694577.aspx
BEHIND THE CURTAIN: STYLES, DOC DEFAULTS, STYLE SETS, AND THEMES
http://blogs.office.com/b/microsoft-...nd-themes.aspx