"Chromatic type is printed from multiple pieces of type, each in a different ink color. The following samples are all from the William H. Page company's 1874 book, 'Specimens of Chromatic Wood Type, Borders, Etc.'[.]. The specimen book was used to sell the wooden pieces of type to printers. The types cost around 25 cents per letter, per ink color.
[In some images you can see] white lines between the [different colors or as part of the letter borders]. That's the paper showing through, and it's an intentional part of the design meant to add another color. Remember, each color is the result of the sheet of paper making a separate pass through the press."
Via Chris Lott