Chartreuse (#7FFF00) is a very light, highly saturated green hue. Chartreuse sits halfway between yellow and green and is named after a French liqueur.
In RGB it is made of 127 red, 255 green and 0 blue. Its HSL hue angle is 90° with 100% saturation and 50% lightness, while its perceptual OKLCH lightness is 89% with a chroma of 0.265. For print, a starting CMYK mix is 50% cyan, 0% magenta, 100% yellow and 0% black.
As a text color on white, Chartreuse has a contrast ratio of 1.3:1, which fails WCAG AA even for large text. On black it reaches 16.21:1 and passes AA for normal text. If you use Chartreuse as a background, put black (or very dark) text on it. The APCA lightness contrast is Lc 89 for black text and Lc -16 for white text.
Its perceptual complement is #F0CBFF, close to periwinkle. Colors that look most similar are neon green, mint, yellow. People with red-green color blindness see chartreuse quite differently (ΔE 16), so do not rely on it alone to signal meaning.