A zucchetto (also called a pileolus) is a skull cap worn by clergy in the Roman Catholic church (and a few other denominations). The different colors of zucchetti (or zucchettos) indicate a clergyman's level in the church hierarchy. I wish I could take credit for this little illustrative number:
This is similar to the Jewish yarmulke, or kippah, which apparently can withstand more creativity and individualism.
I took a closer look because I was interested in the differences. It turns out that zucchetti are created specifically from eight panels that are sewn together, making it somewhat octahedral. (They're also a little larger than yarmulkes.) As you can see from the images above and below, there are much fewer restrictions on how you put a yarmulke together and what you can put on it.