White (#FFFFFF) is a very light, nearly neutral neutral. Pure white is the default page background on the web and the reference point for every contrast calculation.
In RGB it is made of 255 red, 255 green and 255 blue. Its HSL hue angle is 0° with 0% saturation and 100% lightness, while its perceptual OKLCH lightness is 100%. For print, a starting CMYK mix is 0% cyan, 0% magenta, 0% yellow and 0% black.
As a text color on white, White has a contrast ratio of 1:1, which fails WCAG AA even for large text. On black it reaches 21:1 and passes AA for normal text. If you use White as a background, put black (or very dark) text on it. The APCA lightness contrast is Lc 106 for black text and Lc 0 for white text.
Its perceptual complement is #FFFFFF, close to white. Colors that look most similar are off-white, ivory, beige. It looks fairly similar to people with red-green color blindness (ΔE 0), so its meaning mostly survives.