Ships being red below their waterline goes way back to when even the largest vessels were made of wood. You wouldn’t want sea worms eating your hull, would you?
“Why are ships red on the bottom,” has been asked and answered many times but I really liked the animations in this particular explainer video. And, I also hadn’t ever really thought about ship hull coloring until seeing this.
Basically, modern ship hulls being done red is for the sake of tradition. Pretty much any color can be used for the special “anti-fouling” paint vessels are slathered with, but that coating is essential to large ship operations.
As an oceangoing vessel cuts through salt water, it picks up plant life and barnacles and worms that eat hulls. These things can deteriorate the ship’s structural integrity eventually but more importantly, they mess with its hydrodynamics causing it to run slower and burn more fuel.
In the days of sail, shipwrights would use a copper coating or a lead paint with copper oxides in it as a biocide, to keep hulls as drag-free as possible. That copper in the paint gave it its red color.
In 2019, boat-painting tech has advanced to the point at which this stuff can be made pretty much any color. But red is still popular for the sake of tradition, and I suspect because its high contrast with the color of ocean water makes it easy to see the state of a large ship’s load from the outside.
(A container ship will sit lower in the water as it takes on weight, of course.)
In summation, red had copper, copper killed sources of drag, ergo, for once, red really was scientifically the fastest color.