Color in gemstones breaks down into three components: hue, saturation, and tone. Hue is most commonly understood as the "color" of the gemstone. Saturation refers to the vividness or brightness or "colorfulness" of the hue, and tone is the lightness to darkness of the hue.
That is why you have many colours and hues of one type of gemstone.
Find the most popular colour for your zodiac birthstone.