During the play one of the jurors states, “facts may be coloured by the personalities of people who present them.” Which juror makes this statement? What does he mean?

Juror #11 says this. No matter how one tries to be impartial in a situation such as the one portrayed in this story, it is very difficult to remain impartial and speak impartially. He is implying that some of the witnesses and indeed some of the jurors say what they say and speak the way they speak because of their backgrounds and their inborn prejudices.