Bright blue
This color theme is based on Nick Kolenda's color psychology. In the following table you can retrace my color picks: I've picked a bright blue as the primary color and a strong yellow as secondary color for a good contrast. Blue is relaxing, stands for competence and it is also appreciated by booth genders. Although blue should be relaxing, I decided to use a brighter blue, that the user won't get to relaxed and stay focused on his quiz. This bright blue is kind of fresh and should probably activate your brain. The user should be exited about what he is doing and in addition he should think that arsnova.click is useful and should definitely like it. The stronger yellow as secondary color make sure that the theme isn't to dazzling and furthermore stands for excitement and lead to more attention on the content. You can see pictures of the working theme below: