MG, there is more than one strand to this thread and you have focussed solely on the flying suit issue.
What about the expense of swapping to blue overalls that the public won't see anyway?
What about the loss of 'war-fighting' edge? I browsed through the AP today, yup Friday and black flag. Operational support was a reason for bunker wallahs wearing CS95.
CS95 does not aid in individual Service recognition but after 30 or more years of covering up the daily wear of an RAC patrolman doesn't help either. Add an annoymous blue bomber jacket and you disappear completely.
The short lived, RAF blue, zip pocketed, zip fronted No 2 was a distinctive uniform. Aircrew had brevets and some had medals. A modern working dress jacket would enable people to wear their medal ribbons and really stand out from the crowd.
An annoymous woolly pully or annoymous blouson do not look smart and do not help identity. Blue overalls, vice green ones, are a waste of scarce cash.