Engagement rings really can be any kind of ring, but traditionally they are solitaire style which is just one stone on a center setting of some kind. When it comes to solitaire rings, diamonds are more often than not, the choice of stone but could be of any type of stone you want.

Honestly, the ring has more to do with your own personal preferences than tradition. If you want a blue stone then choose a sapphire or blue topaz or aquamarine. Red stones are even becoming more popular and those could be ruby or garnet, one being a more pink and the other a deeper darker blood red. These red and blue stones look quite sharp next to a diamond.

Some couples are opting for a triple stone ring that can stand for past, present and future.
No matter what you decide on, it should be thought that counts and not what anyone else but the wearer wants.