In standard gemmological parlance, the description of the characteristics of an emeralds colour is broken down into three subsections.
Hue – is the denotation of what most would call the colour of the stone. With an emerald it is universally green (whereas for Ruby is would be red), the colour can then be broken down into what type of green it is. These could include the presence of shades of blue or yellow, leading to descriptions like “bluish green” or “yellowish green”.