You may think that naming rail transit lines is a technocratic exercise, and one of the easier aspects of building a transit system. You can either use numbers, letters or colors and move on to the next problem. Sometimes transit agencies make the names too complex to easily understand, but at least the names don't offend anyone.
But like everything else in the world, naming transit lines is more complicated than originally thought. In Atlanta MARTA officials are in trouble over re-naming the line that runs through the Asian-American community the "yellow line." There are a lot of colors in the world, maybe they should have picked a different one.
Sometimes the color has nothing to do with the name but is also contentious. In Los Angeles the new rail line will be called the Expo Line--a diversion from the standard color names--in order to improve the brand of the community it runs through. That was a tough set of negotiations, but only set up the real fight about what color to make the line on the map. As of now the issue is unresolved.