There is more than one type of blue gemstone, which can be set on engagement rings. When it comes to blue stones, you will find a great variety of color and hardness. It is usually not easy to come up with a decision when faced with all the available choices. Pairing It is best to come up with a design that has small diamonds aside from the blue stone. Accent or shoulder diamonds that are white in color will work well, contrasting with the blue stone. This is one reason why halo rings are popular, because they allow encircling the center stone with multiple diamonds.   Blue Sapphire & Diamond Ring Blue sapphires continue to be the most popular choice when it comes to engagement rings. If your budget cannot hold a natural fancy blue diamond, then go with a blue sapphire for a fraction of the price. The latter scores high in durability with a 9 on Mohs Scale.