Finally got around to this post. Thanks for the interest for those of you who shared with me.
I feel quite certain that early batch of Spits were painted deck blue 20B but I do not have access to the tail numbers that were in the batch.
That said, this is a specific aircraft and I did not really like the purple undertone of my paint mix

so I went back to research some more.
This is what I got back from a fellow modeler from Malta. He has researched this subject at length:
Malta Spitfires have always been a topic quite confusing to many who attempt to make the model and it is still an enigma as I can now state for sure that there were a variety of greys and blue greys that was applied to the type after they arrived on board the USS Wasp. In fact the picture that you have sent maybe one of the dark grey used. I am attaching some pictures which I hope will be of help before you decide the final colour. Besides the scourging sun in mid August and the dust which is abrasive at all times take the beat on the Spitfires that survive from day to day.
There is a colour pictures among the ones I am sending which could be best guess. In my opinion it is blue grey (close to dark sea grey) and this replaced the light stone areas leaving the dark earth and grey camouflage on its own while others were overall blue grey. It much resembles the non specular intermediate blue but more on the grey side.
I hope the attached pictures will be of help.
3 years ago we had a Spitfire painted in a somewhat brighter blue which in my opinion was too bluish. I am also attaching one pictures of this aircraft in flight. There are variations in the grey used as you can see from the side views attached.
So I hope you have enough clues to make your choice which I am sure you will not be far from the one that was in use.
So much for a no brainer . . .Back to the can
The next problem is coming up with a color to match . Finally decided on a very old memory of a Shackleton and this is what I came up with.
Even forgot to take any pictures before the coat of Future and the decals.
The next step was trying to match the red. That took more than a few tries :vmad I hate red !
Now, I'm waiting for a decal sheet of numbers to arrive :snoopy Not much to do but wait.
Thanks for looking. Hope you like it. Comments are welcome .
Cheers, Christian B)