Why Hulls are Painted Red

TL;DW: This is “anti-fouling” that repels barnacles, algae, and mollusks by emitting “biocides”. This is desirable because they cause drag (think fuel) and structural damage. Red because traditionally some oxide of Copper.

Also this:

In nature bright colours serve as a warning and to stay away. Ships are very territorial and have even been known to attack people.