Primer lacquering was initially introduced for a specific Purpose, during WW I…to Waterproof the ammunition. The colour coding was a subsidiary matter, and was handy for the machine gunner, who could see the belt (cartridge bases) from behind his gun (Maxim or Vickers or Hotchkiss) to tell what types of rounds were in the belt.
Those countries which did not colour code their ammo primers, still used coloured lacquers to be able to ascertain, at Quality inspection, that the ammo have been correctly waterproofed, and so any colour would do for the US and other countries (who mostly used red or black lacquers). The “tip colours” for “special” ammo came into vogue in the 1920s, to ID ammo with "common "primer seals. (hence the US, and a lot of FN “export” ammo was Tip coloured, to ID special loads.)
With the end of WWII, the “primer colour code” was more or less abandoned, and for most “Nato” ammo producers, a Purplish colour was generally used. The Germans still used Green for Ball, and Red for “Tracer”
(old habits die hard)…one can tell if German technical assistance has been in place with a lot of African and Asian makers of 7,62x51…besides the obvious characteristics of case manufacture, the Primer seals are green or red…just like the German ammo. (seen on Nigerian, Indonesian and Iranian ammo ( 7,62).
Some makers use colour codes to distinguish corrosive from noncorrosive priming (Yugoslavia/Former republics there-of), such as Red for Corr.,Green for Noncorr;
The Chinese use lacquers with abandon, even “clear” ones at times, but these usually match the neck seals as to colours…a common feature of all ComBloc ammo. Ammo type is usually Tip coded.
So what was originally a moisture proofing, turned out to be an ID process by some, and immaterial to others; and just as several contradictory systems developed, it all regressed after WW II to Point coding.
Except in the specific cases mentioned above.
One thing I have noticed with US M1909-style Open-neck-wadded blanks (any calibre) the Wad colour is red, and the primer seal is red ( unless the cases are from “pulled down ball”, then the primer may be black sealed.).
Even the M200 5,56 and the M82 7,62 Blanks are red primer sealed ( the latest "crimped " 7,62 is dark sealed at the point.)
Radway Green L10A2 7,62 blanks are either Green or Wine Red Point-crimp lacquered, but dark or plain lacquered primers.( 1960s dates).
Ah, the variety and mystery of coulered lacquers on cartridge cases.