I don't claim to have made a comprehensive study of the color names in all the available ranges of hobby paint, but off the top of my head I can't recall having bumped into one called "cannon black." The paint companies often adopt labels like that simply as a marketing ploy. I don't blame modelers for getting confused - especially in view of the fact that, nowadays, many of the manufacturers mix matches to colors that are given "official" names (generally by various countries' armed forces). "Dark brown," for instance, is a pretty generic term that can, quite legitimately, mean lots of things to different paint manufacturers. "Dark earth," on the other hand, was the official name of a camouflage color used by the British Royal Air Force in World War II; when a hobby paint manufacturer puts the name "dark earth" on a jar of paint it's fairly safe to assume the contents will match (or nearly match) the RAF color (which actually isn't very dark - unless you compare it with "light earth").
The sailing ship modeler is, perhaps, best advised to ignore those labels and go with his (or her) gut as to what looks right. Whether the color is associated with the RAF, the USAF, the Japanese navy, or, for that matter, the C&O Railroad doesn't really matter in terms of what the finished model looks like. Donald McNarry, for instance, mentioned in an article that he was in the habit of using Humbrol "dark earth" to paint the wire running rigging on his wonderful, small-scale ship models. (For standing rigging he used Humbrol "track color." Whether that refers to railroad tracks or tank tracks I'm not sure.)
Youth, talent, hard work, and enthusiasm are no match for old age and treachery.