This is second hand info so take it with a grain of salt. My engines have always been painted Chevy Orange, even if they weren't that color when I got them.
The different plants phased the colors in at different times. Flint began using the newer Orange-Red after Tonawanda.
Flint engines were the newer color by '70, Tonawanda engines were changed over in '69.
The "Orange" colors are both available from 'Duplicolor';
Chevrolet Orange = #DE-1620
Chevrolet Orange-Red = #DE-1607
The "Blue" engines began getting phased in in 1975 (1976 model year) and there are/were two colors used depending on if the engine was a 'Corporate' or a 'Chevrolet' engine.
The "Blue" colors are both available from 'Duplicolor' also;
Chevrolet Blue = #DE-1609
GM 'Corporate' Blue = #DE-1608
The Chevrolet Blue is darker than the GM blue, which was closer to the old Pontiac Blue ...
GM Blue was used on Detroit Diesels years before it made it to cars.
Ford Blue is darker still than Chevrolet Blue ...
The Black engines began in 1982 in trucks and spread to the cars.
The Duplicolor number is #DE-1613 (Gloss Black)
