Perhaps it was a free-for-all for the transition period between Thornhill acquiring Academy status (Dec 2012) and the introduction of the new grey uniform (Sep 2013).
Some schools have a house system linked to pastoral care. The colour of jumper or tie enables rewards, points and demerits to go to the correct house. Teachers also get a quick clue as to which member of staff to go to to discuss behaviour issues.
This member of staff can then say 'oh they only have a problem with you, it must be how you teach....' but that's irrespective of house, it's down to whether their your chum.