// Jim... how many people of colour were on your University Challenge team? //
None, but in a sample size of four it isn't altogether surprising (I'd also like to point out that I wasn't involved in the selection process, and I'm pretty sure that barely a dozen people tried to join the team anyway). A more interesting question would be how many people of colour were in the overall field, ie the 96 players (and any alternates) from that season.
To an extent, Mastermind (and UC, Only Connect etc) are the wrong places to tackle the issue. It's similar to the Olympics examples, eg "Eric the Eel". What's more important is to try and encourage wider participation at the ground level, eg at pub quizzes, or by creating other quizzing events that allow more people to take part if they wish.