The automatic color is determined by the "Windows Text" color set in Control
Panel>Display>Appearance. Changing this color will affect text color
globally in your windows applications.
Reading between the lines, if you "do not" want to affect font color in any
program but Word, you can do so through Format>Font. Make whatever
specifications you wish, including font color, then click [Default] and
confirm "Yes". If you are prompted to save changes to normal.dot when you
exit Word, confirm "Yes" again.
The function of "Automatic" color is not to control the "default color" but
to control what happens as the background color changes. Black text on a
white background will change to with text "automatically" if the background
is changed to black.