I've got the exact dates somewhere, but basically, the Directive called for the red outline as an extra identification feature, to be in place by September 3rd, I think, then a second Directive cancelled the first, before some units had time to paint the red outlines. By the time it all ended, the red outline had been specified and used for around one month. Many units over-painted the red with blue (in all theatres), which can show as differing tones in B&W photos. Although there were delays in removing the red, due to operational pressures, it was removed from all aircraft no later than the end of September 1943.
Those B&W photos taken after this time, showing a darker outline often mistaken for red, almost certainly show the outline over-painted in blue which, being 'fresher' than the original blue of the roundel to the star, and painted onto the relatively dark base red, would be a darker tone, and easily mistaken for red.