Lots of things

I'm not sure whether or not I'm watching a pull request.

There's a big grey thing that says "watchin" on the top right. Clicking on it changes it from one shade of grey to a slightly different shade of grey. I'm not sure what these shades signify.

Other systems change wording between "watch" or "Start watching" and "watching" or "already watching" so that users can understand the current state more easily.

(If the colours were sufficiently different I could probably, after some training, use the color to tell at a glance whether I'm watching or not, so the colour would be more useful than the words. The two shades of grey don't seem easily distinguishable though, and even after I've toggled colours a few times I still can't figure out which of the two almost-identical shades has what meaning, so I can't train myself to recognise the colours)