hello!!!
On our eight cats, all wear breakaway collars with PLASTIC tags. The tags do not seen to affect the colour of their fur, like I think the brass would. The pastice tags are much lighter than the metal ones(which since I was not aware of plastic tags the cats wore the metal ones for a few years), and the plastic tags do not make the noise that the metal tags made while the cats were eating and the tags hit the food bowls. Even if the cat is indoor only, as our cats are, I have this fear that someday, a guest will keep a door open jut a little too long, and one may get out. They are also microchipped. Yes, this all is an investment, but I think it is worth every penny to keep them safe. Even have collars and tags for when we all go to Cape Cod in the fall!!!
I hope this is of some help, although a tad long....