Amusingly, it’s the uniform, along with the black engineers’ troos and black shoes.
I, however, have been subverting it by wearing a pair of Wranglers all week [until today as mentioned], short sleeved shirts and Airwalks and yesterday the same pants for 2 days in a row by mistake.
I have my own office FWIW, and I was told-off when I was busted sloping about in flip-flops 🙂