Eternity rings are a piece of jewellery that in most cases is worn everyday. This means you need something hard wearing enough to stand up to everyday life. A silver ring may give you the colour of metal that you like, however sterling silver isn't hard wearing enough to stand up to heavy wear, or keep your diamonds secure.
If you are looking for an eternity ring which is silver in colour I would always recommend a Platinum eternity ring. This is because it is hard wearing, hypoallergenic, and because it is a naturally white metal it won't require maintenance to keep its bright white colour, unlike white gold which requires rhodium plating.
If you are looking for a ring which is gold in colour I would suggest 18ct gold. This is because it is made from 75% pure gold, unlike 9ct gold which is only made from 37.5% pure gold, with the majority of it's ingredients made from other metals. 18ct gold has a beautiful warm colour and rarely causes any reactions to the skin.
For those looking for a little warmth from their ring, or to match with a rose gold engagement ring, I would recommend a Rose Gold Eternity Ring.