Self cut and Polised Prehnite Cabochons! Prehnite gemstones are usually light green in color, with a whitish hue or yellowish tinge. Deep green gemstones are not common. Prehnite gemstones often appear cloudy or velvety, and rarely fully transparent, though these gems in particular do have some of that much-sought after transparency. They may also contain colors zones of lighter and darker green.