How about making backgrounds of flag part cells grey, so that white stripes can be shown clearly? Just to make it more beautiful. Also, why blue is accepted for both Dutch and Luxembourgish flags, while red is accepted for Austrian but not Latvian? Good quiz idea, anyway. I love it!
Bolivia's flag includes a symbol in it, so you can't exactly call it a tricolore flag. Also, Latvia's flag doesn't exactly follow the tricolore design because the top and bottom stripes are actually larger than the middle one. Overall, though this quiz is decent!
Good fun! Strictly speaking the German flag's bottom line is gold - the only national flag which officially has gold on it in preference to yellow, I believe.