Just like diamonds and other precious stones, opal is graded based on a variety of scales, including brightness. Precious opal has a brightness scale with four different categories - dull, subdued, bright, or brilliant - with dull and subdued considered the least bright and colorful of the bunch.
Of course, precious opal rings that are rated as "bright" will have much more flashes of color and more variation. Dull or subdued opal is a bit darker and less flashy, which isn't always a bad thing. If you are looking for something more subtle, dark opals are beautiful in their own right.
Think about the way you want your opal ring to look, and how bright and brilliant you want it to be. Explore a variety of opal types to find one that suits your personality, style, and fashion sense.