I did a search on past Forum Discussion on this subject. This one is quite extensive but I copied a bit of it to answer the initial question about "primer color" up to 1925. I'm still looking to answer the second part of he question for:1926/27 . http://www.mtfca.com/discus/messages/118802/126638.html
By Trent Boggess
"A large number of different paints were used on Model T's during the black era. Over thirty different Ford Motor Company specifications for black paint have been identified. (See Appendix A for a list of these paints.) They vary in terms of their chemical composition, the amount of thinners used, the pigments used and in several other respects. For the purposes of discussion, all of these paints can be divided into two categories: oven drying paints and air drying paints. Oven drying paints were used on all-metal parts that could withstand the high temperatures of the baking ovens, such as fenders, hoods and similar parts. Air drying paints were used on dashes and bodies, where the wood contained in these parts would not withstand the high temperatures required to bake the oven drying paints.
The basic oven drying paint for the Model T was what historical sources call “Japan Black”. Why the term “Japan Black” was used to describe the paint is somewhat obscure. Before 1900 “Japanning” was known as a particular type of varnishing that was practiced by the Japanese. It was unique in that after the application of each coat of color varnish, the object was placed in an oven or stove and baked at as high a temperature as possible without damaging the object. To an extent, painting Model T fenders, hoods, and other all metal parts resembles “Japanning” in that after the film of paint was applied the part was baked for up to an hour at a temperature of about 400 degrees.
The term “japan” has second connotation in the painting industry. A particular combination of chemical compounds is known as “Japan Dryers”. When added to vegetable drying oils, as described previously, they reduce the time it takes for the paint to dry. Since “Japan Dryers” were used in making some Model T paints, this too may partly account for the use of the term.
Ford used two japan black paints. The “First Coat Black Elastic Japan” was given the factory specification number F-101 (M-101 after March 15, 1922) and F-102 (M-102 after March 15, 1922) was the factory specification number for “Finish Coat Elastic Black Japan”. Both paints were very similar in composition. They consisted of about 10% linseed oil and dryers (lead and iron dryers were popular in oven baked paints), 55% thinners (mineral spirits or petroleum naphtha), and 25 - 35% Asphaltum. F-101 also contained 1 - 3% carbon black as a pigment, while the finish coat, F-102 contained none"
Towards the end of the thread there is an extensive list of paints & related primers
List of the factory paints used by the Ford Motor Company: 1913 - 1925
Ford # Name Purpose Type
F-101 First Coat Black Elastic Japan Prime coat on Fenders, hoods, etc. Oven
F-102 Second Coat Black Elastic Japan Finish Coat on Fenders, hoods, etc. Oven
F-105 First Coat Brushing Black Japan Front Axles Oven
F-106 Second Coat Brushing Black Japan Front Axles Oven
F-108 First Coat Black Wheel Surfacer Wheels Air
F-111 Red Body Prime Bodies Air
M-111 Quick Drying Black Touch Up General Purpose Repair Work Air
M-114 First Coat Low Bake Enamel Touring and Roadster Bodies Force Dry
M-115 Second Coat Low Bake Enamel Touring and Roadster Bodies Force Dry
M-117 Carburetor Lacquer (Black) Carburetors Air
M-121 Repair Enamel (Low Bake) Repair low bake enamel finishes Force Dry
F-122 Radiator Black Radiators Air
M-124 Empire Gray Metal Primer Touring and Roadster Bodies Force Dry
M-125 Empire Gray Color Varnish Touring and Roadster Bodies Force D