The StackExchange reputation graph looks like it has potential color accessibility problems when showing multiple sites. When hovering over the graph, there are markers with distinct shapes. Great! The graph doesn't rely solely on color! Except:
Nowhere in the legend nor in the tooltip is there a mapping between shape and site, so using distinct shapes doesn't actually help.
The tooltip bubble partially obscures the markers anyway.
You can see in the above screenshot that ordering of items in the tooltip doesn't help either.
It'd be better if the tooltip and the legend showed the marker shapes and if the tooltip were offset a little farther away.
I'm using Firefox 68.0.2 (64-bit) on Windows 7 x64.