The additional complexity to support multiple colors doesn't seem worthwhile. More importantly, though, the use of different colors implies that the bars differ in some fashion (e.g., represent different data), which isn't accurate in this case.
Different colors might be useful for reports with aggregated data, such as a report for all instructors with instructor scores further subdivided by course(s) taught.
The additional complexity to support multiple colors doesn't seem worthwhile. More importantly, though, the use of different colors implies that the bars differ in some fashion (e.g., represent different data), which isn't accurate in this case.
Different colors might be useful for reports with aggregated data, such as a report for all instructors with instructor scores further subdivided by course(s) taught.