There are different ways to change the
color of your displayed font,
depending on how the font is used.
GUIText & Text Mesh If you are using a
GUIText or a Text Mesh, you can change
its color by using a custom Material
for the font. In the Project View,
click on Create->Material, and select
and set up the newly created Material
in the Inspector. Make sure you assign
the texture from the font asset to the
material. If you use the built-in
GUI/Text Shader shader for the font
material, you can choose the color in
the Text Color property of the
material.
UnityGUI If you are using UnityGUI
scripting to display your font, you
have much more control over the font's
color under different circumstances.
To change the font's color, you create
a GUISkin from Assets->Create->GUI
Skin, and define the color for the
specific control state, e.g.
Label->Normal->Text Color. For more
details, please read the GUI Skin
page.
As zoon pointed out, you need to create your own custom font material and use that.
The reason is that we don't allow editing of imported assets, only of the import settings - otherwise, this would be a sure way of breaking things when using external version control. However, having an option for font color in the font importer seems like a very reasonable request, though.