HD and Verci - by "blue collar", I referred to an attitude, not a mode of dress! ATCOs in the UK are (mostly) union members, and the recruitment pool used to be school leavers rather than graduates.
For those joining today, ATC may well be an alternative to law, accountancy or engineering, which was not the case in, say, the 1960s and 1970s. Perhaps "blue collar" was the wrong term, and if so I apologise. However, my point about the attitudes of some of the old salts is valid.