Fits perfectly on Neutrik connectors, the dark red color makes it more subtle and less eye-catching than other bright colors, but it is highly noticeable if you want to identify the cable.
To put it on you will need to unscrew the connector barrel and replace the stock one, usually black. This ring won't fall of or move along the cable, it will always stay lock onto the connector making it permanently marked without using labels that leave glue residues.