There is a great deal of interest in knowing what colors are used in a website. For this reason, a site's styling guidelines are usually quite detailed. The problem is that a site's styles are likely to change over time, and if they don't change, then they are likely to stay the same. Even if there is a change in the site, it is likely that some colors will remain in the same place.

This is the same with the colors declared in a CSS file. Different resources in a CSS file are used for the same purpose, so they all are similar in color, but differ in appearance. If you need to create a more meaningful color index, you will be able to browse the styles to see which ones use which colors and why they are similar.