Opal is one of the most beautiful of gemstones. These stones can flash every color of the spectrum with a brilliance that can even surpass that of diamond. Precious opal ranges from clear through white, gray, red, orange, yellow, green, blue, magenta, rose, pink, slate, olive, brown, and black. Of these hues, the reds against black are the most rare, whereas white and greens are the most common. Some rare specimens produce brilliant color flashes when turned in the light.