Your guess is as good as mine

If Stanaway's to be believed, the painting of the front part of the spinner, in the dark blue for the 431st only was done for a short time while they were on Dobodura.
I suppose another possibilty is that the ones showing a blue spinner for the 431st were some of the hand me downs from the 39th FS and they didn't remove the blue spinners that the 39th FS had and just added the red band?
There is one profile in Possum, Clover and Hades that shows the red band on the blue nose of an early 431st bird.
Guess we'll never know for sure unless we can find one still parked in the jungle somewhere with the paint still on

Dan/CorkyJr