RAF colours

I always thought it was supposed to be a recognition feature - if one wing is black , he's on my side - apparently works for the other side too - kind of like tracers - they work both ways also.

it also creates a fuzzy effect to the eye, by breaking the wing outline.

It was done for recognition from the ground, i.e. for anti aircraft gunners.
Some aircraft still carried the markings into 1941. On the black wing the roundel had a yellow outline, even when the wing was repainted, in some cases the outline was left in place.
Pete

Hi Albertsponson
B&W undersides in 1941? I would like to know where you are getting your information? These markings were discontinued in June 1940. Maybe you are confusing these markings with the port black wing and sky undersides introduced 27th November 1940. The underside roundels were retained and the spinner was painted Sky along with the introduction of the fuselage band. The black port wing was repainted Sky as of 22nd April 1941. Certainly not Black & White.
Cheers
Bob S.

Oops, I misread the text in an old Michael J F Bowyer book. It shows Hurricane P2627 in mid '41 with the two colour underside. The 'other' colour is given as 'probably a shade like duck egg green'. DOH!
In mitigation I plead the early hour of the day, it's 0630 here, the only time you can get a decent net connection over here!
Pete