I'm a biologist and I use viruses (adenovirus to be specific) to insert genes into mammalian cells in vitro. I do this to study the function of said genes. To make a usable stock of virus, I infect a small number of viruses into particular cell line, wherein the viruses replicate and give me an 'amplified' stock.

When I harvest the amplified viruses, I use a centrifuge to separate them from the rest of the cellular crud. The viruses separate into a distinct, narrow, blue-white band in the centrifuge tube. It seems that concentrated virus has a distinct color, despite being made up of colorless viral particles.

How can this be so?

The title is a little confusing, but the article just describes how one virus particle can't have any visible color because it's too small. A substance made of lots of virus particles is like a substance made of lots of atoms; of course it's possible for that to have a color.

I think that was alluded to with the example of the staples in the microwave. It's reasonable to extrapolate that the same principle applies to viruses in aggregate when dealing with visible light.

What a great article. Thanks for posting.