Emerald (#50C878) is a light, moderately saturated green hue. Emerald is a jewel-tone green, Pantone colour of the year in 2013.
In RGB it is made of 80 red, 200 green and 120 blue. Its HSL hue angle is 140° with 52% saturation and 55% lightness, while its perceptual OKLCH lightness is 75% with a chroma of 0.158. For print, a starting CMYK mix is 60% cyan, 0% magenta, 40% yellow and 22% black.
As a text color on white, Emerald has a contrast ratio of 2.13:1, which fails WCAG AA even for large text. On black it reaches 9.87:1 and passes AA for normal text. If you use Emerald as a background, put black (or very dark) text on it. The APCA lightness contrast is Lc 63 for black text and Lc -46 for white text.
Its perceptual complement is #E584D9, close to orchid. Colors that look most similar are pistachio, lime green, kelly green. People with red-green color blindness see emerald quite differently (ΔE 13), so do not rely on it alone to signal meaning.