(click image to enlarge)
Note that the foreground colours are used for rare, uncommon, common, epic and mundane, while the background colours are used for artifact, relic, mythical, legendary and magical. The default background colours are all "none", as I don't personally like having text with background colours, but from a functional perspective it could be very useful for players who (for example) are only interested in collecting rare artifacts, etc.
You can see a little white label at the bottom of the text window containing the text "look collar". That's actually the mouseover message - my mouse pointer doesn't show up in the screenshot, but that's what you get when you hover over a link.