You will see a lot of red, white and blue this Independence Day weekend. Contrary to popular opinion, however, these colors on the flag have no official symbolic significance. The Flag Resolution from the Second Continental Congress on June 14, 1777, specifies nothing but "Resolved, That the flag of the thirteen United States be thirteen stripes, alternate red and white; that the union be thirteen stars, white in a blue field, representing a new constellation."
To this day, the official reference colors of the flag are applicable only to flags produced by the federal government. Flag vendors can--and often do--use their own interpretations of red, white and blue. The official colors, used by the government, are specified by reference to the Standard Color Reference of America, 10th edition, a book containing colored fabric swatches produced by The Color Association of the United States (CAUS). Note that these colors are only applicable to cloth. It is impossible to precisely convert them to RGB for display on a monitor, or CMYK for printing.
Although the flag’s colors have no symbolic meaning, they are a natural derivation from the Great Seal of the United States, which was commissioned by the Continental Congress the day the Declaration of Independence was signed, and does have an official statement on the symbolism of the colors. The Secretary of the Continental Congress, Charles Thompson, declared:
The colours of the pales are those used in the flag of the United States of America; White signifies purity and innocence, Red, hardiness & valor, and Blue, the colour of the Chief signifies vigilance, perseverance & justice.
Wikipedia, Great Seal of the United States
The seal is actually more important than the flag, which is why its creation was embarked upon as soon as independence was declared, while the stars and stripes had to wait another year. Since ancient times seals have been used to ensure the authenticity of governmental decrees. The Great Seal of the United States was designed for the same purpose. Ironically for our purposes, the official seal used to stamp documents is monochrome.