The score is made up of two parts; social score and skills score. A colleague is awarded a maximum of five points for each. Any colleague scoring less than six is not a good colleague. For example …
Nice but dim: Social score 4 + Skills score 1 = 5 Not a good colleague
Evil genius: Social score 1 + Skills score = 5 Not a good colleague
In both these cases the colleagues would only need to improve their poor performing area by one point to make the change to Good Colleague. The Good Colleague Score allows for a wide variety (36 in total) where the circumstances are less extreme, where a colleague is average at their job and fine to get along with, which would score you a 4 and highlight room for improvement.