[Image Source] FLASHBACK
This is a zebrafish retina (eye) that is stained with an antibody that recognizes double cone cells (photoreceptors). It has also been stained with other things to recognize different layers, which is what gives you the colors you see above. When antibodies are used for staining, this is known as immunohistochemistry (immuno- referring to the immune reaction that creates an antibody and histo- referring to the tissue being stained). Antibodies are made by injecting the purified protein you want to look at into an animal and collecting the antibodies that are created by the animal’s immune system to target and get rid of the protein. You can then tag these antibodies (so they will show up as a specific color) and put them over a tissue slice, where they will attach to the protein in the tissue and show you where it is located.