This can be done in Outlook by choosing Tools, Options, Mail Format, Editor
Options. You'll see the drop down for the 3 color schemes offered under the
Popular category.
Also, this is an Office wide change. If you make this change in any Office
2007 program it will apply to all Office 2007 programs. For example, In Word
2007 choose Office button, Word Options, make the change under the Popular
category.