Toward the end of World War II, the complex Navy camouflage scheme for carrier-based aircraft was gradually replaced with an overall Sea Blue color. However, the national insignia was retained intact. This provided examples that directly compare Sea Blue and Insignia Blue. (Note that the colors may not have been accurately depicted in the original that I scanned, much less on your computer screen.)
It was eventually suggested, probably by Grumman, that the Insignia Blue surround of the national insignia was redundant and should be eliminated on all-blue airplanes. It was reportedly deleted well before the official authorization to do so was issued in June 1946.
A red bar was added in January 1947 to reinstate all the colors of the U.S. flag.*
(This F4U would appear to have spent some time ashore in its recent past...)
I like the color in the picture above but it appears to be lighter and bluer than Sea Blue color chips from Elliott, et al. Here are the current Federal Standard colors (Insignia Blue = 15044; gloss Sea Blue = 15042) according to Colorserver:
The sea-blue story is complicated by the fact that according to Dana Bell, "There were two completely different versions of ANA 623 Glossy Sea Blue. Citing the instability of the original pigments, in 1947 BuAer reformulated the color and issued new color chips. Modelers have been arguing about this for years, not realizing that some of us have the early chip (on heavy card stock) and others the newer chip (on a metal plate). The newer chip is indeed darker and is also a bit greener."
*Note that action with respect to authorization often occurred in due course. How else to explain this F4U national insignia that still has the Insignia Blue surround and also the red bar?
The picture is obviously too green; here is an auto correction, which looks about right:
That the bar is faded may be indicative of it being added in the field with paint at hand.
My impression is that Grumman painted overall-blue F6Fs with paint that didn't fade as dramatically.