The US flag is remarkable that the blue color in it is much darker blue, used in the flags of other States. Officially this shade of blue is referred to as the Navy Blue (Navy Blue). It is understandable from a practical point of view: in XVIII century was not yet persistent dyes and «normal» blue quickly выцветал would pale blue; the flag of thick, dark blue long retained their properties. For the same reason, red on the American flag also darker red flags of other countries, though not to the same extent.