By activating multiple fluorescent proteins in neurons, neuroscientists at Harvard University are imaging the brain and nervous system as never before, rendering these cells in a riotous spray of colors dubbed a “Brainbow.”

This is from a few months ago but apparently it hasn't been cited here. The Nature article, Transgenic strategies for combinatorial expression of fluorescent proteins in the nervous system, is available in the Google cache. The editor wrote:

The 'Brainbow' technique can paint hundreds of individual neurons with distinctive hues, producing a detailed map of neuronal circuitry. This technology should not only boost mapping efforts in normal or diseased brains, but could also be applied to other complex cell populations, such as the immune system.