In nature, most cells are transparent and without color. Animal cells that have a lot of iron, like red blood cells, are deep red. Cells that contain the substance melanin are often brown. It is the absence of melanin that makes eyes blue. Scientists have tricks for making different parts of cells glow with fluorescent dyes. These colors are artificial, but beautiful.
The vast majority of the cells in your body are clear, because the molecules they are made of reflect all wavelengths of visible light. However, several types of cells do have color. These include the red blood cells, the cells in the iris of your eye and the cells in your skin. Red blood cells are red because of a molecule called heme, which contains an iron atom. Cells in the eye or skin can have different colors because they contain different amounts of a molecule called melanin. The more melanin in a cell, the darker it will appear.