Bingo chaps
From the trials boffin:
“Those panels were certainly gloss white. They were there before Aero Flight acquired the aircraft and there were 3 panels on the leading edge of each wing and I think six on the leading edge of the fin. I understand that they were sprayed on before the V-Bombers were repainted white (with pale roundels) to reflect the flash from exploding nuclear bombs. Their purpose was to test paints provided by various manufacturers before the contract was placed. They seemed to be equally satisfactory as none ever to my knowledge ever stripped back from the leading edge. They were useful in that one could easily tell Aero Flight's XA890 from BLEU’s XA899.