@JordonBiondo provided the answer. Here are some alternative, related ways to do the same thing:
default, to set its foreground to that color.
default-frame-alist, to set its
background-color to that color.
These all do the same thing. Face
default correponds to the default settings for frame parameters
Using Customize has the advantage that it type-checks things, preventing simple typo mistakes and other, more important mistakes. And more generally (not in this case, however), it manages things like initialization and updating triggers.
Using simple assignment code in your init file does not handle these things (but it is often sufficient).
If you do use Customize (which you can do interactively, with the Customize UI, or from your init file, using
customize-set-variable etc.) then I recommend that you define option
custom-file, so Customize uses a separate file and doesn't mess with your init file. Just load
custom-file from your init file.