Colour coding calendar blocks

How do I change the colour of calendar blocks without changing the background colour?

I want to colour code certain events, for example, I am creating a timetable planner for students of different years. And wish to colour code by the different years, so year 7 will show up yellow on the calendar block, and year 8 will show up blue.

Can you share link to page where you use Caledar block? We can help easier.