The birthstone of December, the intense deep blue color of a london blue topaz ring can evoke thoughts of warm Caribbean nights. The birthstone of December, the intense deep blue color of a london blue topaz ring can evoke thoughts of warm Caribbean nights. This birthstone of October has a luminosity and glow that makes an opal the treasure that it really is. The rainbow of colors on a neutral white background makes an opal ring a perfect match for any outfit.