Thanks all for the good comments

To answer some questions:
John - the brackets are photo-etched (actually they are from the Eduard D.VII.... is that cheating??

)
Stephen - good point on the brackets - I thought about this a little bit, as the PART set shows brackets fitted to the lower wings also. In the end I thought "these will help cover up my mistakes!!"
RAGIII - Excellent point, I didn't really think that the dark portions could have represented the white areas overpainted - I didn't really think to check against pics of other Jasta 6 fokkers to see if the stripes corresponded, I simply went with the AG instructions and the photo which confirms the supposed locations of the black stripes - however I can now see that the opposite may have been plausible.
That said however, if the white stripes were painted over before the whole tail was painted over in grey-green, why would they still appear darker in the photo? The only way this would happen would be for them to be painted over in a darker colour, and it don't get much darker than black - if the original black was faded and the white stripes painted over in a heavier black as you have alluded to, even with over-painting I don't think you would still end up with that much of a contrast. If the whole tail was painted in grey-green and THEN the previously white areas painted in black, then perhaps you would get the effect in the photo?
That all said, whatever the reason, these areas are darker in the photos, and I have painted my model according to the locations in the photo and the AG instructions - I am interested in your thoughts!
BC