Make non-existent value states readable.

[jmduke]

See #10.

So I realize in my dumb hindsight that the issue isn't the regional values themselves, it's the interaction between fillColor and color as the individual regions are styled: basically white on white. My proposed solution is to give a default outline of light grey, so states can always be seen:

I think it also makes sense that borderColor could be a configurable value (via url params), and could include that as a separate PR.

Since this is a bit more design-y than my prior hopes of it being a simple configuration issue, I understand if you have some reservations! Lemme know what ya think.