The following morning after sailing to join the San Pablo, Shirley is explaining to Jake how she became interested in becoming a missionary. She tells him that Reverend Jameson showed color slides in the basement of her church. This film is supposed to take place during 1926. Agfachrome (slide film) was not manufactured until 1932 and Kodachrome not until 1935.
shareAll true, but the reference is probably not to film slides, but glass slides (hyalotypes) which were projected with a magic latern (as the projection device was called). Glass projection slides had been around since the mid-19th century in black and white and Agfa had perfected a process for producing color glass projection slides in 1916, well in advance of the film's mid-20s time frame.
shareYes, they had autochrome glass slide.
http://en.wikipedia.org/wiki/Autochrome_Lumi%C3%A8re
The glass slides used in the projectors were also often hand colored.