Thanks a lot for your kind words!
I agree that the feedback could be better. It currently shows you the next color for two seconds, but it's not too clear at first. I did originally intend to give audible feedback in parallel to the visual feedback but didn't have time for it.
I have seen this issue with scrolling up/down before, but I'm not sure what causes it. I suspect a focusing issue. Maybe I can do something about it after the voting period.
Which browser did you use and does the problem disappear if you click into the game window?