Black (#000000) is a very dark, nearly neutral neutral. Pure black has the maximum 21:1 contrast with white. Many designers soften body text to a near-black to reduce glare.
In RGB it is made of 0 red, 0 green and 0 blue. Its HSL hue angle is 0° with 0% saturation and 0% lightness, while its perceptual OKLCH lightness is 0%. For print, a starting CMYK mix is 0% cyan, 0% magenta, 0% yellow and 100% black.
As a text color on white, Black has a contrast ratio of 21:1, which passes WCAG AA for normal text. On black it reaches 1:1 and fails AA. If you use Black as a background, put white text on it. The APCA lightness contrast is Lc 0 for black text and Lc -108 for white text.
Its perceptual complement is #000000, close to black. Colors that look most similar are gunmetal, midnight blue, navy blue. It looks fairly similar to people with red-green color blindness (ΔE 0), so its meaning mostly survives.