The range of hues allowed for a beryl to be called emerald is quite narrow as stones must have a dominant green hue which can be modified by blue or small amounts of yellow. The tone and saturation must also be sufficiently deep for gems to earn the title of emerald. With all things considered, gems with yellow are less valuable than those with pure green or some blue. The most valuable color is a bluish-green hue with strong to vivid saturation and medium to medium-dark tone, but different people are drawn to stones with different variations. Some like gems with a lighter, less formal color. Others prefer gems with more of a cooler blue influence. In the end, you should select your emerald jewelry based on your personal color preferences!