When the line first opened in 1938, to distinguish the simultaneous formation of the three lines instead of one, colour-coding was introduced. The first one, the Sokolnicheskaya being Red, for mostly political reasons. However chronologically the Arbatsko–Pokrovskaya line would have been second and was coloured blue, whilst the third one Zamoskvoretskaya was given green. However as part of the Arbatsko–Pokrovskaya line was already in operation from the first stage, the significance of the Zamoskvoretskaya line was far greater. As a result the line was listed second. This tradition has since been passed on in all ex-Soviet cities with the first line being red and the second/third being either blue or green. However some metros, notably Minsk Metro chose to deliberately reverse the trend.