There is no official assignment of meaning or symbolism to the colors of the flag.
However, Charles Thomson, secretary of the Continental Congress, in describing the Great Seal, related its colors to those of the flag.

According to Thomson,
"White signifies purity and innocence,
Red, hardiness & valor,
and Blue . . . vigilance, perseverance & justice."

So the Red and White stripes of 13 represent the link
to the original ground of 13 states on which the nation has been built up.
And the stars, representing the union of now 50 states,
have been laid on the blue canton to bind all of them
with the bond of vigilance, perseverance and justice.