Fair enough. I understand where he is coming from.
However, at the time of Dunkirk, the 109 fighter units had, in the main, the light blue undersurfaces carried almost to the top of the fuselage sides, in contrast to the solid two-tone camouflage of the RAF fighters. There was therefore quite a difference visually between the two nation's fighters. It was only later, in mid-August 1940, when instructions had been received by the 109 units to apply green/grey mottle to the whole of the fuselage sides, that the problem of quick identification occurred in the air, and hence the instruction was issued to paint the engine cowlings rudders, wing tips in yellow, to try to prevent 'friendly fire' losses.
Hope this explains things OK for you.