From the conversation Professor White's hair can't be white (for then it would match his or her name), nor can it be black because he (or she) replies to the black-haired person. Therefore it must be brown. If the lady's hair isn't brown, then Professor White is not a lady. The remark from the black-haired person can't be from Professor Black (for then the color of hair would match his or her name) and can't be from Professor White as well (because the remark prompts an exclamation from White). Therefore the black-haired person is Jean Brown. Based on this the first statement from the lady is made by Professor Black. Her hair can't be black or brown, so she must be blonde.