Small town American movie; changes from black and white to color as the people liberate themselves?

If I recall, it takes place in a small town in the 50's or early 60's. People could only see in black and white, but start seeing colors in their clothing, lipstick, cars, trees, etc. until the whole town is in color. I believe the mayor holds a meeting in the town hall to try to convince others that it's an outrage.