We often see artistic representations of animals that have long been extinct. Some of these are in color, even though we only have the fossils. Fossil expert Maria McNamara explains how scientists try to infer their coloration. She says that they carefully study fossil metallic insects with hard shells that have preserved their color as fossils to see what makes them take on various colors. She says that if an animal’s skin layer is fossilized, that helps too. When it comes to dinosaur colors, she says:

We have various feathered dinosaurs that we have melanin in these color patterns for, and in modern birds, melanin coloration is modified by other pigments. These other pigments aren’t preserved as fossils, so we cannot be sure for now.

If we found dinosaur skin that was really well preserved, we would have a good chance of reconstructing color in more detail. The problem is that most dinosaur skin is preserved as impressions. There are a number of examples where you actually retain a thin organic or mineralized film, but even though a few have been studied, none have actually yielded details of the pigments.
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Ten years ago, the whole notion that fossils could preserve color was hardly on the radar—there was only one study out. Twelve years ago, no one would even know that this was possible.

There are several mass spectrometry techniques that look at the molecular fragments on the surface of your material, but not all fragments are diagnostic. There are chemical techniques that produce unique fragments of the melanin molecules so you can’t confuse them with anything else. People are also looking at the inorganic chemistry of fossils and trying to recover supporting evidence of color.