The Watson family in Christopher Paul Curtis' The Watsons Go to Birmingham—1963 drive a 1948 Plymouth. Kenny, the book's narrator, describes this vehicle as, "dull brown," while Byron more colorfully states that it is "turd brown." This car was given to Kenny and Byron's father by Uncle Bud two years prior to the start of the novel, when it was already thirteen years old. It's a car that has been well taken care of, but is not always the most reliable in the harsh winter climate of Michigan.
This car is central to the plot of the book because it enables the Watsons to get out of Flint, Michigan after Byron begins to act out and make poor decisions. These behaviors motivate the family to move Byron to Birmingham, Alabama for the summer, where he will live with his Grandma Sands. The Watsons travel in the Plymouth down to Birmingham, but eventually choose not to stay there after the 16th Street Baptist Church is bombed by members of the Ku Klux Klan in a truly horrific episode of racially-motivated terrorism.
I have attached below an image of this make and model of car.