There are many ways of arranging bars of colour, other than as a rainbow. In fact, colours aren't actually needed at all - shading and patterns work just as well.

As long as the structure has some kind of distinguishable bars to let the eye connect a marker at the side with an attribute name at the top, the mechanism works.

And there are other potential applications beyond font management.

Here are some examples of other 'skins', and other applications.

A Digital Asset Management application ("DataRainbow")

A gallery format for images is no problem

Classical Architecture

Seaside cottages

Pinstripes

Liquorice Allsorts (a somewhat less formal approach!)

Front-end for Google (this would combine bookmark and search functionality)