Striking the colors is the universally recognized indication of surrender, particularly for ships at sea. Surrender is dated from the time the ensign is struck.
In international law
"Colors. A national flag (or a battle ensign). The colors . . . are hauled down as a token of submission."
International law absolutely requires a ship of war to fly its ensign at the commencement of any hostile acts, i.e., before firing on the enemy. During battle there is no purpose in striking the colors other than to indicate surrender.
It was and is an offense to continue to fight after striking one's colors, and an offense to continue to fire on an enemy after she has struck her colors, unless he indicates by some other action, such as continuing to fire or seeking to escape, that he has not truly surrendered. It is for this reason that Raphael Semmes spoke with bitter sarcasm about USS Kearsarge's continuing to fire after CSS Alabama had struck her colors. For this reason, striking the colors is conclusive evidence......