A colorless sapphire or topaz would be classified as a colored stone. In spite of the wording there are only two categories, diamonds and everything else. There are a couple of terms commonly used for gem material that is created in a laboratory. Homocreate refers to materials that duplicate their natural counterparts. Emerald, sapphires and spinel are common homocreates.
Synthetic materials have no counterpart in nature.
Cubic Zirconium was long thought to be a synthetic, but tiny crystals have now been found in nature. While natural and man made materials can share the same physical and optical properties, there are still considerably differences, the main one being rarity. A natural gem takes considerable time to form and is usually millions of years old. While natural and man made materials appear nearly identical, their values vary considerably. For this reason it is important to be able to distinguish between the two.