|by Jean Livet, Harvard University|
In 2000 Jeff Lichtman and Joshua Sanes began playing around with the neurons of mice, and after crossing different genetic lines, created mice with three different shades of cells, blue, green and yellow. By 2007 the Brainbow technique was developed.
|Tamily Weissman, "Brainbow” transgenic mouse hippocampus (40X)|
The Havard Gazette describes the process in full detail if you're interested.