Red, White and Blue theme: "All American"?
There is precedent for the 'Red, White and Blue' theme in British automotive (racing) history. When Singer fielded a team of 1.5 liter cars for LeMans in the early 30s (1934, I think), they assembled 3 cars whose colors were red, white and blue. Known affectionately as "This, That, and 'Tother" they had nothing to do with the American market. Conspicuous was the absence of what we now think of as British Racing Green, however this was before the fixed attribution of particular colors being associated with specific countries.
The Union Jack is comprised of red, white and blue. Is it reasonable to assume the Brits were thinking of both 'us' and 'them' in sending over a red, white and blue trio of Harrington LeMans cars to introduce the new model? I think it can be seen both ways.
As the release was for the LeMans model commemorating the Index of Thermal Efficiency win by the works team Harrington, 3000 RW, it's conceivable --if a bit of a stretch-- to think the red, white and blue motif could have been selected to acknowledge the LeMans Index win, flouting the French national flag colors into the bargain, by the Brits thumbing their noses at the French. A little back story: the Index was created to offer the smaller, less powerful cars --read the French makes, like Panhard-- a chance to win something. In 1961, when the Brits took the win, it was very significant: the purse was greater than that awarded the second place finisher.