"Hey, they really came?" The corpulent captain's tone was unusually relaxed, seeing that the visitors meant harm, yet he bore an expression as if he had an ace up his sleeve, "Raise the flag, raise the naval flag."
Sailors climbed up the mainmast, the blue and yellow striped flag symbolizing the Sea Blue Republic was taken down, replaced by a striking red diagonal cross flag fluttering in the wind.
This flag represented the Vineta Navy; the blue symbolized Vineta, the red symbolized blood, and the meaning of the flag was that the navy had established the Sea Blue Republic with blood.
But in reality, the true reason for choosing red back then was because the flag's designers thought it was more conspicuous and could be recognized from afar. The interpretation involving blood came later, eventually turning into a misconstrued fact that became the official explanation.