Looking at photos (the basis for my beliefs) it just appears to me that the color of the 109 is darker than the tropical green. The 109 was sunk shortly after relocating to Rendova. I'm including a photo of PT-107 taken at the time it was in route to its new base at Rendova. This would be the same color as PT-109. These two boats were in the same squadron and would have the same resources available. I've also included a photo of PT-103 which was also taken at exactly the same time which looks the same as 107 if not a darker photo.
I acknowledge that what I'm about to say is very unscientific. I took the photo of Robey's boat and converted it to a black and white photo. Comparing the two the 107 looks much darker. It looks like a darker green with lots of scuffing and weathering.
I have posted in this forum some modeling tips for the 109. These are based on what I pulled out of Donovan's book PT-109 and the two known photos of 109 when Kennedy was in command. If you have trouble finding them let me know.
I exchanged emails with a gentleman that removed the paint from PT-105 after the 109 sank and he told me that the color was "forest green" whatever that means. Forest green to me means dark green much like what is on the Revell box except with more weathering.
Just for grins I've thrown in Hollywood's version of the 109. A member of the 109 crew played a roll in this movie and was a technical advisor. Is this the right color? It looks a lot like John's MTB Green. Darker still I think. I've also tossed in a photo of JFK in the cockpit of the 109 which you can find all over the internet.
We'll never know for sure what the actual color looked like in the field and sorry if I'm just confusing the issue more. John and Al's information is extremely well researched and you're not going to be wrong following their advice. I'm still undecided on what to do about the finish paint on my model. I keep hoping that some miracle photo will appear but I doubt it. I'll probably end up going with some variation of dark green or perhaps MTB green. I'm building a 1/48 105 boat so maybe both. Best of luck!
Dave