Blue (#0000FF) is a dark, highly saturated blue hue. Pure sRGB blue is very dark perceptually: white text passes contrast on it, black text does not.
In RGB it is made of 0 red, 0 green and 255 blue. Its HSL hue angle is 240° with 100% saturation and 50% lightness, while its perceptual OKLCH lightness is 45% with a chroma of 0.313. For print, a starting CMYK mix is 100% cyan, 100% magenta, 0% yellow and 0% black.
As a text color on white, Blue has a contrast ratio of 8.59:1, which passes WCAG AA for normal text. On black it reaches 2.44:1 and fails AA. If you use Blue as a background, put white text on it. The APCA lightness contrast is Lc 18 for black text and Lc -91 for white text.
Its perceptual complement is #6E5000, close to chocolate. Colors that look most similar are sapphire, cobalt blue, denim. It looks fairly similar to people with red-green color blindness (ΔE 5), so its meaning mostly survives.