The red paint was the anti-fouling paint that contained a compound known as Tributyltin (TBT).
TBT based anti-fouling almost always came in red as the chemicals in the paint would give it a red colour. The paint could be obtained in other shades, mainly black, blue or green. Usually the non-red based versions were not as good as preventing fouling.
TBT based anti-fouling was banned from use in the early to mid 90s in Australia as far as I can recall, and probably every where else in the world because of its toxic properties that would leech into the water and marine life.
I worked as a shipwrights hand in a boat yard (private company) and we had to stop using this paint, but when our boatyard got the contract to do some maintenance on some Navy work boats, the Navy would supply the anti-fouling paints from their own stores (we would source all other paints and materials). 50% of the time the paint was red, and 50% of the time it was black. According to the Navy guy who would drop it off, the black anti-fouling was surplus from the submarines. The black stuff was required to be painted on in double the application coats as the red as it did not last as long.
Quite often, our foreman would order more of the TBT based anti-fouling from the Navy guys for the job (they supplied it and paid for it), because it was not available to be bought as it was banned. I suppose the Navy was exempt. The foreman would then get us to paint our boat yard work boats with "the good stuff", the left over paint. Our boats would resist fouling for 3 to 4 times longer than other boats with regular non TBT based anti-fouling.
Im sure since then, the improvements in anti-fouling paint have improved and it would be non TBT based. This would mean that the paint could be any colour, and that is why subs and surface ships almost always have black anti-fouling now (for low visibility too).
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