You chose Choice Two, which is what actually happened. Thomas changed into regular clothing whenever he walked to Dr. Blalock's office.
Wearing a suit and tie would be more acceptable and less conspicuous when visiting the administrative building.
Thomas will feel less distracted and conspicuous as he walks to Blalock's office.
He avoids the unspoken appraisal that he is acting "uppity."
Thomas will maintain an air of professionalism while not attracting so much unwanted attention.
Changing clothes whenever Dr. Blalock summons him is inconvenient and time consuming.
He may attract just as much attention in a suit and tie as in a lab coat.
He is subsuming his pride in wearing the coat for the relative anonymity of street clothes.