I've been an aircraft mechanic for thirty years and still use zinc chromate where the aircraft mfg tells me to. The use of zinc chromate became widespread in the late 30's and early 40's because of the US military especially the Navy. They were used primarly as an anti-corrosive and secondarly as a primer.
As noted, the chromate came in two basic colors, green and yellow. Early testing found that if yellow chromate was used where it could be seen by the flight crews, (ie, cockpits etc), it had a tendency to make a large percentage of those people violently airsick under a wide range of conditions, causing green to be used in those areas.
In the late 40s the Navy ran some tests and determined that while the cromates worked as an anticorrisive, they were no where as effective as a coat of epoxy paint (greys in the cockpits and whites in other areas (landing gears etc). The latter also made locating liquid leaks (hydraulic fluid etc) much easier.
Light aircraft aren't usually chromated. There are a number of reasons for this with weight and expense being for most. If you completely chromate a Cessna 150, you can increase empty weight by as much as 20 lbs, which is a significant amount for that plane and increase the price of the aircraft by as much as $1500 dollars (or more). The only civilian light aircraft that I know were chromated during construction were those aircraft produced as seaplanes or amphibians.
As far as corrosion on aircraft that are based in a salt water environment (within 50 miles of the ocean), it's always a problem. However, the worst corrosion I ever observed in aircraft was in a group of C-150 trainers that had been operated out of an airport on the shores of Lake Michigan between Chicago and Milwaukee. We ended up and had to condemn about a third of them.