Question: What are the most common “line colors” for transit lines? I’ve heard of blue lines, red lines, yellow/green/silver/purple/orange/pink lines, but is there anything I’m missing? Once a transit system gets over that amount of colors, do they usually switch to Line 1/A Train/etc.?

Answer: To answer your question, I’m going to point you towards Nick Rougeux’s excellent “Global Subway Spectrum” web page, which breaks down the route colours used by rapid transit systems around the world very comprehensively. I featured it on Transit Maps back in 2013, but Nick’s made some improvements since then, including giving RGB hex values for all the colours. Design resource, anyone?

The most colours used by a single system that Nick has listed is 15, for the Seoul Metro. This is closely followed by the Paris Metro and the Beijing Metro, both of which use 14 colours. Overall, red, green and blue lines are the frontrunners, although the spread around the colour wheel is actually surprisingly even. There’s also quite a lot of variance between different interpretations of the same colour: one system’s “Orange Line” can be decidedly different to another’s, while “blue” can range from light cyan all the way up to deep navy.

Once the number of colours becomes unwieldy, there are a couple of choices that can be made. You can group routes by their main trunk line with all of those lines sharing a common colour (like the New York subway map does), or simply reuse some colours for shorter lines that don’t interact with each other (the Paris Metro map uses this technique).

Bus maps – which often have far more routes than rapid transit maps – are increasingly using colour to denote service type (regular, express, limited, etc.) rather than individual routes, which greatly reduces the number of colours required.