Yeah
I think the problem is the whole episode was never documented at all. Most 'decisions' have to be based on pictures and the general concensus of opinion.
I think the which blue debate will go on long after we've shuffled off the mortal coils, lol.
Never seen a picture which shows any Malta Spit with really light uppers indicating a really light shade of blue though.
I think this comes from - some bombers (Beauforts?) on the way to deployment were given two tone blue uppers (Dark and Light Mediterranean Blue) at Alexandria MU.
Early guesses to which blue relied on that to try and figure out which blue was used.
Found this snippet from "Merlins Over Malta"
When the aircraft were put aboard the USS Wasp they were wearing standard camouflage schemes but on the deck of an aircraft carrier sailing through the Mediterranean these camouflage patterns offered no protection. The solution was to paint the top surfaces of the aircraft blue. Paint was taken from the stores and applied to the aircraft. There is no definitive colour match because paint was mixed and watered down to ensure there was enough to go around.
Backed up by a guy whos Grandfather was RAF groundcrew on USS Wasp -
My late grandfather was an RAF ground crew member who was put on Wasp to maintain the Spitfires and prep them for the flight to Malta.
Both my father and I remember him saying that the Spitfires were painted with deck paint from the
US stores during the voyage. I remember him also saying that they repainted them several times on the way, and were quite surprised when they actually took off due to the extra weight of the paint! I suspect they were delivered in desert camouflage, I seem to remember him saying that at one stage there was some green added to the scheme.
I also remember him saying that the underside was repainted at least once, but I couldn't say what colour.
Unfortunately by the time I was old enough to realise this was "significant" information, his memory wasn't sufficiently good to recall it.
So basically pick a blue that would have been available on-ship and knock yourself out

.
249 sqn in Malta continued painting their aircraft in non-standard colors.
Do a search youll find many many threads on it and discussions if it was actually even blue at all.