In my opinion their is no known correct dark green color for early Palmer Bros engines made between 1895 and about 1912 when the switch to dark gray was undertaken. Again we have no precise dark gray color for engines made by Palmer Bros. or the successor company, The Palmer Engine Co. between 1912 and 1957. We do know that from the 1920s until about 1957 the paint was bought from Baltimore Paint. Baltimore Paint was bought out and its records destroyed in the late 1950s. The dark gray paint was bought in 55 gallon drum lots and no precise color chip was ever specified or expected. The color of the few existing new old stock Palmer parts that are painted dark gray is a very close match with Valspar Porch & Floor enamel "DARK Gray".

From about 1957 to 1973 when The Palmer Engine Co closed its doors the best match with the green on existing engines with seemingly original green paint is X-O Rust, Safety Green sold in TRUE Value stores. 

The few known engines sold after 1973 by successor companies seems to have been a Ford Blue.

It is suggested that a Dark green such as Hunter Green in a Polyurethane Enamel would be a good choice for engines made prior to 1912. It is made by General Paint & Manufacturing Co. and sold in True Value stores. It should be kept in mind that this color is only a guess and any choice of dark green would be just as good.

Red was not a Palmer Bros. or The Palmer Engine Co. color as Red was Lathrop's color. Lathrop was their principal competitor. 

There is no known existing evidence that primers with different colors were ever utilized on any model or any vintage engine. It is quite likely that fillers were used to cover cosmetic imperfections in casting. It is likely that this practice ceased during WWII. It would be interesting to know if any post WWII production show any evidence of this practice.