OK Jack, what if you have come into work in blues, knowing definately that you are not on the flypro, you go to metbrief....
Straight after, the DA identifies YOU as the only available pilot to fly a task due to your qualification/chum's off-sick/ etc......
If you've got a rush job: route to plan, NOTAMs to check, flight plan to write, etc, how extra rushed and maxed out are you going to be when you realise you have to go to the locker room and change??
You might waste 10 minutes (or thereabouts)?
In this situation, that's the kind of distraction you do not need.
Fine, wear blues for groundschool, SDO, parades, etc.
But for god's sake, if there is even a sniff of a chance of flying, pitch up in grobag every time!