The only sphere of activity I can think of where blue is a colour (and so are yellow, green, brown, pink and black), but red is not a colour is the game of snooker.
I recently watched the World Snooker Championships on the TV and it suddenly struck me as strange to hear utterances like: He’s hit a red and not a colour. However, the game is home to some strange words anyhow, beginning with its own name. Apparently, this derives from obsolete British Army slang. A snooker was a beginner, an inexperienced soldier. Legend has it that British Army officers in Jabalpur in India around 1875 had the idea of adding coloured balls to a game called pyramid pool, which already had a white ball, a black ball and a pyramid of red balls. This new variation got its name, apparently, when, some years later, a player missed an easy shot and someone called him a snooker.