The <u><em>white color</em></u> has been used historically by <u><em>health professionals</em></u> (nurses, doctors, etc).
Based on this familiarity with this particular color (white) and doctors, our subconscious automatically links or relates them each other, so if Nina saw an advertisement containing health information, where was being offered a product of this kind, she will automatically trust on the person word, even if he/she is not a doctor, all this due the mental process mentioned before.
So assuming that she is interested in the product offered by the person in a white coat, trust and confidence will be generated automatically in her towards the commercial, due to the mental process she makes relating the white color with a health specialist.