Well If I were you, I would color the points themselves. And follow the coloring scheme HN already uses (lighter grey for weaker and darker grey for stronger) I

Well If I were you, I would color the points themselves. And follow the coloring scheme HN already uses (lighter grey for weaker and darker grey for stronger) If the points become unreadable due to very low score, user can always double click on it and it will highlight in blue background.