acred,
Yes L7003 PS-L was for real,during the Dunkirk evacuation 264 Squadron had it's moment of glory,and on the 28th May 1940 L7003 shot down a Bf109,it was piloted by Plt Off Michael Young,the gunner was LAC S B Johnson.
This before the 109 pilots realised there was a gun turret mounted on the plane,thinking it was just another Hurricane,imagine their shock when coming up on the Defiants six and being presented with four Browning's staring at them!
They sooned changed tactics on attacking Defiants and during the Battle of Britain would come up to attack from below,thus rendering the Defiant helpless.
During this early period the RAF adopted the half black,half sky colours on the underneath of their aircraft wings,during the Battle of Britain they then resorted to the underneath of the wings being painted back to Sky,or Eau De Nil,although on some aircraft the order to repaint was not undertaken,due probably to the ground crews being somewhat busy!!
All information was taken from two great books,Defiant,Blenheim and Havoc Aces by Andrew Thomas,and the best one,Mark Ansell's superb book Boulton Paul Defiant.