Okay, this is very minor as bugs go, but it's been happening to me for over a week now so I think it's worth noting. Sometimes when I switch colors, it doesn't switch right away.
Example: I am drawing with green, then switch to blue. The Blue circle is encapsulated by red, indicating that it is now the active color. I begin drawing my "blue" line and it is green for about 2 second, then switches to blue.
Like I said, it is a minor thing, BUT when I am really pressed for time, and drawing a complex panel, it kind of sucks to keep hitting undo, especially when my second try is not as good as the first.