I need some help and hope that you guys n' girls can answer the questions I have.

I plan on building the USS Thetis Bay CVE-90 in 1/350 as in the picture below, which dates from around Sept 44. Her deck is laden with 8 x PBY's, 18 x F6F and a Grumman Duck, all are stated as war wary / damaged and are being returned to the US from the Pacific theatre. The Hellcats are gloss Sea Blue except two which appear to be three colour Sea blue over intermediate blue over white, some have coloured rings on the front of the cowling, yellow, white, red?
The PBY's appear to be intermediate blue over white judging from the star n'bar being darker but what's the dark patches on the wings?
The Duck I believe is intermediate blue over white.

So can any one help with those colours?

The dark patches on the wings are likely from two sources. Around the engines it's oil and grime and along the spar and the other spots are likely spot repaints where the new paint isn't as faded as the old.

Thank you Jessica you have confirmed my thoughts on the PBY's now just to work out the cowl ring colours on the F6F's.

Luciano,
Interesting shot you've go here, I might be able to add a little info. I just had a similar question a week or two ago about some cowling colors on an AT-11. Colors are always questionable, depending on which type of B&W film used in the 1930's and 40's. While one can never say never on these things, I'd be very doubtful of red being you're cowling color since these are Pacific aircraft. Red was almost never used in markings on US Naval aircraft in the Pacific to avoid confusion with the red national insignia used on Japanese aircraft. A comparison of the cowling ring colors on the Hellcats with the known white on the national wing markings show a marked difference in tone, even with similar lighting conditions. I'd say a best guess would be yellow. There are known instances of yellow being used as a unit identifier on F6F's in the Pacific, so it would fit. That's my spin.
Carry on

If they're in overall sea blue, the cowl rings would most likely have been white for operational aircraft.

Jess,
I concur that around the engines is most likely oil and grime, but along the leading and trailing spars, I'm not so sure it's just paint, as each PBY has basically the same coloration. It's almost like they attempted to seal off the inside of the wings at those spars. Perhaps it's to keep out the saltwater spray from further damage to the wing interior structure.
Joel

Oh dear, have I opened up a can of worms?

Don't forget that from the rear spar back the PBY wing is fabric, so that's likely a long piece of rib tape with fresh dope on it keeping it sealed.