The idea is, that text is great when you come to the UI for the first time. But, as you use the software every day, it's slow to read the text, so your eye becomes accustomed to the icons and you can use them as a shortcut to save yourself having to read the text. The icons should all be different shapes (as the eye sees the outline of a shape the quickest), be different color (but not only different colors as some people are color blind). I think this used to be common UI knowledge but I remember reading it in design guidelines for the original Mac OS X 10.0.

Somehow this has all gone wrong through: no text so the first time you use it you've no idea what the icons mean, they are all the same color and pretty much the same shape so you don't even get the speed of recognition.