Purple (#800080) is a dark, highly saturated magenta hue. Purple has signalled royalty since Tyrian purple dye was made from thousands of sea snails.
In RGB it is made of 128 red, 0 green and 128 blue. Its HSL hue angle is 300° with 100% saturation and 25% lightness, while its perceptual OKLCH lightness is 42% with a chroma of 0.193. For print, a starting CMYK mix is 0% cyan, 100% magenta, 0% yellow and 50% black.
As a text color on white, Purple has a contrast ratio of 9.42:1, which passes WCAG AA for normal text. On black it reaches 2.23:1 and fails AA. If you use Purple as a background, put white text on it. The APCA lightness contrast is Lc 14 for black text and Lc -94 for white text.
Its perceptual complement is #005E23, close to hunter green. Colors that look most similar are plum, indigo, eggplant. People with red-green color blindness see purple quite differently (ΔE 18), so do not rely on it alone to signal meaning.