Introduction
Looping within a Custom Transformer is a perfect tool for making FME Art. Here is an example created simply to see how looping works:
In order to change workspace parameters, run it by pressing Ctrl+R, otherwise it will run with predefined parameters, which make a nice picture, but always the same. Feel free to play with it, to modify it in any way and if you get something amazing, don't be shy, share your Art with the FME community.
You may also find useful an algorithm for creating values for fme_color (or fme_fill_color in this case) attribute, which would spread evenly from dark to light independently on the number of input features.