Long waits for DH while he waits in the non-EU passports queue at airports have given me the opportunity to see how passport control officers differentiate their treatment of people with white and brown skin. DH (white, Australian) sails through when he gets to the front of the queue. Almost all the people held up have brown skin.
A friend of mine, who originally came from India, lives in the US. She sometimes stops over in Britain to see me on her way to India and, until she got a US passport, she was regularly given a hard time at passport control. Basically, they wanted to know whether she was trying to immigrate into Britain illegally. Since she is a Professor at a major US university, with a Harvard PhD, this is unlikely, but did not impress our friends at passport control. 'Is your friend English', one of them once asked her? [no prizes for guessing the implications of this question.] 'No, she's Welsh', she replied. This didn't go down well and he exercised his discretion to charge her £50 for a short-stay visa.
My favourite passport control story relates to Prof. Amartya Sen, a Nobel-prize winning economist. He was stopped at passport control at Heathrow a few years ago. When he gave his address as 'The Master's Lodgings, Trinity College, Cambridge', they asked whether he was working there on the domestic staff. He had to explain that he IS the Master of Trinity.