Turner Classic Movies had the movie "Will Success Spoil Rock Hunter?" on recently. Did any of you catch it? It's from 1957 and it has probably the most different colors of soft plastic 500 sets of any movie I've ever seen. It was released in July, 1957, so all the phones are in the early colors.
The movie stars Tony Randall and Jayne Mansfield, with Betsy Drake, Joan Blondell, John Williams and Henry Jones. It was directed by Frank Tashlin, who also directed Looney Tunes cartoons at Warner Brothers, and there's a distinct cartoonish quality to the movie. It's very fast paced and full of sight gags and double entendre.
I made some screen shots to show the phones. The first picture is Rockwell Hunter's secretary's office, with a green keyset with gray cords. The second picture is the boss' secretary's office with a dark beige keyset. Also note the early model IBM Executive typewriter with carbon film ribbon (sitting vertically on each side). The third picture is the TWA terminal at the airport and a black 500. The fourth picture is the conference room at the office, with a mahogany brown 500! Now it's getting really good. I included front and back views. The fifth picture shows a pay phone. More to follow.