Hippocampus: Broad Overview; image credit: Tamily Weissman, Jeff Lichtman, and Joshua Sanes, 2005, as featured in Discover's The Brain Is Ready For Its Closeup and Portraits of the Mind: Visualizing the Brain from Antiquity to the 21st Century by Carl Schoonover.
"This image of the hippocampus was created by breeding mice carrying different variants of the GFP gene - not only green fluorescent protein, but also its red and blue counterparts. The result? Simultaneous visualization of several different classes of neurons in various layers of the hippocampus, laced through each other like multicolored fingers." (via Bioephemera)