Imagine a Where’s Waldo book with nothing but black and white pictures. Good luck using his candy-stripe sweater as a visual cue. Now you know what it’s like trying to find a virus on a greyscale microscopic image. Microbiologists have dealt with this problem for decades, because when things get small, things go dark. Photons, bits of light essential to discerning color, are too clunky to resolve anything much smaller than say, a synapse connecting two neurons. If you want to look at things like viruses, bacteria, or molecules passing through cell walls, you must use an electron microscope.

The devices, developed in the 1930s, use electromagnetic coils to bombard a chemically-prepped, vacuum-sealed specimen with, you guessed it, electrons. The resulting image is more like a shadow casting than a photograph, with the particles revealing shapes, depth, contours, and texture. But not color. Which sucks, because color is an excellent way of finding things–important things–hidden in an image.

Finding all those microscopic Waldos will be much easier, because investigators at the Center for Research in Biological Systems at UC San Diego developed a method for adding color to electron microscopic imagery. The method, published today in Cell Chemical Biology, involves two key technological developments: Treating specimens with rare earth metals, then examining them under a special type of electron microscope typically used to analyze novel synthetic materials.

The colorizing process starts like normal electron microscopy. Electrons like metal, so the microscopist treats the specimen with a heavy metal, like lead, then creates a greyscale image–the base layer. The next step is treating the specimen with different types of rare earth metals called lanthanides (also used in lithium-ion batteries). Lanthanides are pickier than heavy metals and only stick to certain molecule types, which makes those the only molecules the electron microscope sees. The microscopist processes the image, assigns the layer a color–say, green–and layers it on top of the grayscale base layer.