Dark blue. For example, many schools and universities, such as monash in Australia and many middle schools in Britain. You can see that their badges are all this color. Many British people call them royal blue. This is a rigorous and lively color.

Of course, you should be rigorous in your study and use dark colors, but because you are a class and a lively student, you can't lose your vitality. You can add other colors on a dark blue background.

I suggest you refer to the badges of various schools.

This is a very orthodox color. Without losing the atmosphere.

If you write it, as long as it doesn't conflict with blue. For example, yellow is also good. Although ordinary, it is very atmospheric and comfortable.