I've primed plenty of bits over the years in light pink primer on boats, never thought about the reason for the colour before. Primer often zinc silver, light pink or a mustard-green colour, usually Jotun or International tins. Antifoul (proper stuff, not now) used to be in some bright colours also -probably reflecting it was full of the not so nice stuff effective at keeping growth off. Red top coat I guess even now weathers quite quick, back in the day I could guess a matt red maybe weathering to matt or pink relatively quickly in some light?