Made indicators have full alpha. Changed some background highlights to b...

Purely a matter of taste, but I made the alpha values full for all indicators. I figured that it was more in keeping with Base 16's idea of (a) bold colours and (b) a set of 16 consistent colours. Note that this means some of the background highlighting indicator styles needed to be converted to outlines, which I realise might be a bit controversial (since it's getting into the realm of actual UI changes).