What shade of blue is the color blue mailboxes used by the United States of America?

Many of us know are the names certain shades of color, and their names are used by industry and commerce, for example, when a person orders a touch up or paint sample kit to a vehicle. What blue is the color used by the U.S. post office? I'd say blue. Is that correct? Maybe there is a more technical name or other name for the color blue? And the blue of the American flag behind the stars, also navy blue? And where does this word, etymology, or history?

I would describe Post Office of America as the royal blue (a clear, dark blue - a color that signifies royalty) Identify and color as Navy Blue (dark blue - the color of the uniform British navy).

Sequin American Flag Box