I thought the quiz overall was pretty interesting. That question had me scratching my head because I came up with three possibilities, and I had to guess which was the simplest. All of my solutions involved the correlation between the shape and its color.

“Odd one out” questions are almost always too ambiguous, because it’s actually really hard to come up with a set of four things where only and exactly one has something different about it from the other three, unless three items are absolutely identical. A better way to use the concept would be to ask for explanations of why each item can be considered the odd one out.