Zhao, Y. et al. Science advance online publication (8 September 2011).

Single-color genetically encoded calcium (Ca2+) indicators have so far only been available in a green color. Zhao et al. now describe improved green, blue and red Ca2+ indicators. To generate these tools, they screened large libraries of GFP-based Ca2+ indicator genetic variants for large Ca2+-dependent changes in fluorescence. These tools open the door to imaging calcium signaling in multiple colors in single cells and in Caenorhabditis elegans.