Anonymity is important in retrospectives because it helps establish trust and feelings of psychological safety. While you can view who is currently present in your retrospectives using the side navigation panel on the left, the content of retrospectives is completely anonymous.
Each note in Retrium is a different color, which is randomly generated from a selection of 17 color options. Two notes of the same color did not necessarily come from the same retro participant.
During the private brainstorming phase, you'll only be able to see the content of your notes. This is to reduce groupthink and maintain anonymity. Once you move on to the Group phase everyone will then be able to see all of the cards without knowing who created which cards.
True anonymity makes Retrium a valuable option for distributed or co-located retrospectives because you aren't able to identify who wrote what based on the color or size of the note, the person's handwriting, or any other distinguishing feature. The best ideas can be considered without being influenced by who wrote them.
The colors of notes can be used to make it easier to discuss which one you're talking about, speeding up grouping and helping people focus their attention to the right place quickly.