They sing it in the beginning of the movie and say it alot before they fight with the french...
It means to raise their flag that they've designed up.
It means to raise the flags. Because the flags show their colors. Whether they are the Army or the Pirates.
The term colours refers to the colors of a countries flag. Many times during that era ships would sail without showing their countries flag so as not to be easily recognized by enemy ships. Often they could sneak up on an enemies ship and then hoist their colors....a prelude to engaging in battle. Ships would not battle without signifying what country they belonged to. Pirates would often spot a specific ship...note what country they were from and hoist that countries flag so that they could get close without suspicion. Then they would run up the JOLLY ROGER (pirate flag) and attack. For whatever reason they always showed their affiliation just before a battle...I guess that made it more honorable
