Design 2

I did try to use SVG from image service but no nice cross-browser SVG/libsass friendly (libsass tries to execute `invert()` when used inside `-webkit-filter` and fails :disappointed:) way to invert the colours.

The tint property in the image service also didn't seem to do what I wanted... maybe I needed a "fill" option?

Anyway.  This felt the simplest/least awful option.