Thanks for the encouragment guys!
Another productive day today on the cobra. I didn't avoid the gardening today, but I still managed to mask and spray the OD, so some progress to report.
I masked up and sprayed the rudder, elevators and ailerons for a coat of faded olive drab - It was very common for these surfaces to fade out quickly. If you look at the colour pic I posted previously, the cobra coded "S" at the head of the line up shows this quite distinctly, so I was after this effect.
Once those where sprayed I re-masked for the normal Olive Drab and sprayed that. It appears dark under un-natural light, but when under bright light it shows the pre-shade clearly. I'm happy with the result, so next it's the yellow stripe theater markings.
Cheers
Peter