It may not be useful for anything, but you can use HTML markup in collection names, as well as CSS through the style attribute and element. Unfortunately, this isn't very practical as there is a limit on the collection name length.
It will only render when you are on the homescreen , inside the collection, or deleting a collection. I haven't tested this, but it should also work with metadata such as title, author, or series. I can see this having potential use when combined with calibre.
Using this you can produce some interesting results, particularly when using an <img> tag. Once the filepath is sorted out, it will actually display an image. Still, it probably doesn't have much actual use for Collections.