Alexandrite would be the color change stone. It will change to purple in the candescent light and in the natural light it will turn a bluish red. However if it is color changing and it changes those colors it is synthetic. Natural alexandrite will change from Red and green. The red and green is worth a lot of money. The synthetic still is collectible and desirable but it's a mix of sapphire and amethyst. If it is in Alexandria. Tomorrow morning go outside and see if it's a different color in the natural light.