added banners for location with color

@ltw. Here's a screenshot of our progress with Pairing is Caring. http://i.imgur.com/ZYABghQ.png?1

We implemented background colors and "enbiggenated" the font for mentor availability locations. Now hopefully people won't schedule sessions for cities they don't live in. Yaaaaay.
`city_tag_background_color` maybe? `background_color` is a little too generic.