RAF fuselage roundel yellow outer surround.

[T-21]

Not a daft question, but why was this colour used ?  at the time of the Munich crisis they were painted over. 

[alt-92]

What timeframe are you referring to? 
The yellow outer ring re-appeared in several iterations. even on 2TAF upper wings after Jan 1945.

 

In May 1940, the yellow outer ring was ordered to be added back to fuselage sides (along with the introduction of fin flash) to make the markings more conspicuous.

[wellsprop]

http://woodair.net/Aviation/roundels/RAF_Roundels.htm

 

IIRC, the conspicuous yellow outer rings were initially removed as they were though to be too conspicuous. It soon became clear that being conspicuous is actually quite helpful when things get a bit chaotic (i.e. Battle of Britain).

 

As @alt-92 has pointed out, the yellow rings were also painted on the upper wing roundels (and sometimes lower) of 2TAF, as again things became a bit confusing in the air, during the death throes of the Luftwaffe (and even encounters with the Soviet Air Force).

[Graham Boak]

The upper wing roundels remained without the Yellow - these are the ones that would be visible (if any) in photo-reconnaissance work.  The history of aviation is full of clashes between the competing demands of low and high visibility - camouflage vs markings.  Which is most important when.  Part of what makes the subject so fascinating.

[Graham Boak]

I don't doubt it.  However. such work was rare to non-existent in April/May 1940.  The Luftwaffe relied upon vertical cameras from some height - as indeed did most nations.  It was some time before the values of fighter aircraft in this role, with sideways-looking cameras, was recognised and even then oblique-mounted cameras appear to have been rare in the Luftwaffe.  It would not have been of any concern to the Air Ministry at that time.  There was certainly no low-level reconnaissance of UK airfields.

 

I would also suggest that in the event of such photos existing (perhaps from the French campaign), the circumstances in which they were taken would have meant the presence or absence of a yellow ring was irrelevant.  If a yellow ring could be seen, then the aircraft would already be plainly identifiable as a Hurricane, Lysander or Blenheim.  Or Morane, Dewoitine, Lez Mureaux.

[Graham Boak]

In peacetime, only a very comparatively small number of civil aircraft will have got anywhere near militarily useful targets in the UK in order to carry out low-level oblique photography of any military value.  A small number of photos taken over a wide period of time from hand-held cameras would be of little military use.  This requires widespread and repeated operations.  The Germans certainly did create a fine library of vertical photos of RAF airfields and other military targets in the UK, but these were largely taken by their Dornier 71Ps.  Despite this, German intelligence of RAF deployments and strengths is commonly described as poor. 

 

The Germans split their photographic work between the Fernaufklarer with Dornier 17P on deeper penetration flights and vertical cameras, and Nahaufklarer doing close tactical work with the Army using hand-held cameras on Hs126s.  With the exception of hand-held, these principles largely continued throughout the war with improved aircraft types.  However, even with the adoption (after 1940) of fighter-type aircraft in the PR role they largely operated with vertical cameras.  The Germans failed to adopt the low-level fighter-reconnaissance role in the same way as the Allies did, with side-mounted cameras on P-40s, Hurricanes, P-51s, P-38s and Spitfires.  Possibly this is at least partially because of the success of the Fw.189 in the Nahaufklarer role on the Eastern Front, whereas such a type in Allied hands would have very low survivability.

 

The low-level raid on Kenley was months after the decision to go to yellow surrounds.   As such, it was irrelevant.  None of the Dorniers carried fixed oblique cameras.  Opportunistic photos taken on raids would be of little intelligence value (except perhaps purely by chance).

 

Camouflage goes down the sides because of its value in wartime against low-level attacks.

 

All of which is irrelevant to the main point.  The Ministry ordered Yellow surrounds for visual identification when in the air.  If visibility on the ground was ever considered a problem, this could readily be taken care of by the adoption of covering sheets.  As indeed was seen elsewhere at various times in various Air Forces.   Such measures can safely be left to local authorities.  Other measures such as dispersal were far more significant.