It came up this week with this map on poverty and deprivation in London, part of our London: the data series. Recently we've been using the colour scale on the map below, which is a variation on the famous traffic light collection of colours - for the Guardian, this tends to go from green, meaning good, or low - up to red, meaning bad or high. It's used by map makers and newspaper designers all the time. But is it any good?
This sparked a debate on Twitter, with Gregor Aisch of Driven by Data weighing in on the weaknesses of the colours we chose. It led to a big conversation - and a mutual editing of the map's colours.
The Storified converstaion is worth reading.