What's the point of allocating colors to the classes?

By default, the colors used on all timetables are those of the subjects. You can also allocate colors to classes, and use them on teacher and staff timetables: go to My preferences > Grids > Contents of the courses; in the first drop-down menu, select the type of resource concerned (for example, Teachers); then, in the second drop-down menu Courses' colors, select Classes.