Indigo (#4B0082) is a dark, highly saturated purple hue. Indigo is a deep blue-violet dye from the indigo plant, famous for denim.
In RGB it is made of 75 red, 0 green and 130 blue. Its HSL hue angle is 275° with 100% saturation and 25% lightness, while its perceptual OKLCH lightness is 34% with a chroma of 0.179. For print, a starting CMYK mix is 42% cyan, 100% magenta, 0% yellow and 49% black.
As a text color on white, Indigo has a contrast ratio of 12.95:1, which passes WCAG AA for normal text. On black it reaches 1.62:1 and fails AA. If you use Indigo as a background, put white text on it. The APCA lightness contrast is Lc 0 for black text and Lc -101 for white text.
Its perceptual complement is #313E00, close to taupe. Colors that look most similar are midnight blue, ultramarine, purple. It looks fairly similar to people with red-green color blindness (ΔE 12), so its meaning mostly survives.