Looking at the enlarged photo, I do think the nose is yellow. OK, it's a lighter tone than the deep yellow of the roundel, but then it's a) fresher paint. b) a washable distemper, and c) almost certainly a different shade of yellow, and relatively thinly applied.
Look closely and compare with the white in the roundel, and there is a difference, slight, I'll admit, but a different tone.
I remember seeing the photo, as it was quite striking, and the caption, or article, mentioned the exercise, and the approximate date(s).
I might still have the magazine - or it might actually be in my copy of 'Combat Codes', come to think of it - so I'll have a search when I get back from Duxford.