Magenta (#FF00FF) is a light, highly saturated magenta hue. Magenta is not in the rainbow: your brain invents it when red and blue light mix without green. It is one of the four CMYK printing inks.
In RGB it is made of 255 red, 0 green and 255 blue. Its HSL hue angle is 300° with 100% saturation and 50% lightness, while its perceptual OKLCH lightness is 70% with a chroma of 0.322. For print, a starting CMYK mix is 0% cyan, 100% magenta, 0% yellow and 0% black.
As a text color on white, Magenta has a contrast ratio of 3.14:1, which passes AA only for large text and UI parts. On black it reaches 6.7:1 and passes AA for normal text. If you use Magenta as a background, put black (or very dark) text on it. The APCA lightness contrast is Lc 48 for black text and Lc -61 for white text.
Its perceptual complement is #00BF4F, close to kelly green. Colors that look most similar are orchid, hot pink, rose. People with red-green color blindness see magenta quite differently (ΔE 30), so do not rely on it alone to signal meaning.