Red and green are the "traditional" colors, though much like karle94 I tend to draw boats with antifouling pigments based on national colors and such. Red is the more common of the two in general.
During the latter 19th century there was a particular type of German-origin paint (sometimes called "Rahtjen" paint after its inventor) that was commonly used by the Royal Navy, which was red. The American Tarr & Wonson Company and the Italian Moravia company also produced red antifouling coatings in the same period, but with different methods.
The actual active ingredients have nothing to do with the color, it's just a fashion statement based on frugality for the most part. In the 1800s the most common biocides were mercury and arsenic, with some unknown addition of copper from the cuprous/cupric oxides used (I mean, people knew copper was a biocide obviously, but they still put arsenic and mercury in the paint because they assumed the copper wasn't going to leech off adequately). Red pigments were just fairly cheap for coloring in the form of copper(I) oxide and red lead, as was Paris green later in the 1890's and 1900's, and navies in the tail end of the Age of Sail and beginning of the Age of Steam had relatively little standardization in this regard. They tended to buy "commercial off-the-shelf" paints in fat lots from factories directly, instead of having factories mix their orders to official standards or chromatic metrics, as that sort of color standardization doesn't appear until WW1 and more fully in WW2. There were probably white antifouling paints I guess, as I think white lead would be a fairly cheap pigment at the time. Perhaps you could do blue or mauve if you wanted to be flashy and flex a synthetic dye industry.
Without added pigments the more typical color of a antifouling paint is red, black, or grey, depending on the additives, which you see in austere situations (the RN in WW2 wartime destroyers occasionally used grey or black antifouling coats). The pigments were really just added so painters could tell if they've applied an even coat tbh. Aside from maybe cupric oxide (which can be any number of colors from green, red, orange, black, grey, blue, pink, and probably more), I guess, they wouldn't contribute much to the actual efficacy of the coating though.
t.
https://darchive.mblwhoilibrary.org/bit ... r%2011.pdf