Correction to: Nature Methods https://doi.org/10.1038/nmeth.1618. Published online 27 May 2011.

In the version of this article originally published, the color palette discussed in the third paragraph was missing a link to a presentation by Kei Ito and Masataka Okabe (2002), which is now available at https://jfly.uni-koeln.de/html/manuals/pdf/color_blind.pdf.