http://cartography.uni-muenster.de/en/symbols/color-and-color-schemes
https://www.mapbox.com/tilemill/docs/guides/tips-for-color/ http://gijs.github.io/blog/2013/10/24/using-color-in-maps/ http://geo-pickmeup.com/the-hidden-meanings-of-maps-design-and-colors/