There's a display issue while looking at any(?) quiz list. If you've played more than 50 of the list, it won't mark those as being played. As an example, for me only the first 50 quizzes in this list come up as green, despite having played some of the last ones as well:
http://www.funtrivia.com/special_lists.cfm?quizlist=967

May be a setting on your computer - I see all 58 on the first screen.

I see the same thing that looney sees