Lots of grist for the mill here and let me give you some more information on my thoughts so far:
The #10 car was built in a matter of weeks from a crashed Nash-Healey coupe. Here's a portion of an email I received from the late Healey's chief engineer, Roger Menadue, about that process:
“With less than 2 weeks to go I said that I could make another car body and all. Donald and Geoffrey both said, “Impossible, nobody could build a LeMans race car complete with body in less than two weeks.” I said, “Maybe not, but I can.” They said, “Don’t be ridiculous.” I said, “You two will not have any say in the building, either. I can’t have people arguing. I will never get it done.” They knew that they couldn’t argue with me and had to give in. They were furious especially Donald and more so when I had it ready on time. But worse was to follow.”
“In the Race, my car beat every other car in the race including one of the three works Mercedes. I beat the Ferraris, the Jaguars, Astton Martins, Cunninghams, Talbots. You name them, I beat them.”
I first saw the car in 1986 after it had been restored by Hyannis Restorations on Cape Cod, Massachusetts and at that time it was Healey Blue. Donald Healey was there at the time and was quite happy to see the car again. I wasn't aware of him saying, "Oh God, they got the color all wrong" but he was also very circumspect about criticizing the restorations of our cars he saw back then. It was later restored by Redline Restorations in Connecticut, also in Healey Blue.
I like to rely on period sources in my research and the most likely ones I've seen so far are the racingsportscar archive shows both the 10 and 11 being "light metallic green"
The black and whie photo of 10 and 11 would be the best source if it only was in color. As to other "period" photos of the cars in color, we just don't know whether they have changed color over time. I can stare at some of them and convince myself at one time it's green and another it's blue.
The Spark model is a wild card, it appears neither light metallic blue nor light metallic green.
Another issue is this was a race car that did 24 hours as LeMans. It was eventually shipped to the US to be displayed at Nash dealers. Did they respray it after the race? The second photo shown by Jager looks like a darker color. Was this picture taken in the US or at a European show before it was shipped to the US? There's some palm trees in the background but I can't make out the lettering on the placard, Here's a picture of the car on display at a Nash dealer in Massachusetts, of little help.

I'll add to the thread if I find anything new