Cobalt Blue (#0047AB) is a dark, highly saturated blue hue. Cobalt blue comes from a cobalt salt pigment and is strong, saturated and reliable.
In RGB it is made of 0 red, 71 green and 171 blue. Its HSL hue angle is 215° with 100% saturation and 34% lightness, while its perceptual OKLCH lightness is 43% with a chroma of 0.172. For print, a starting CMYK mix is 100% cyan, 58% magenta, 0% yellow and 33% black.
As a text color on white, Cobalt Blue has a contrast ratio of 8.44:1, which passes WCAG AA for normal text. On black it reaches 2.49:1 and fails AA. If you use Cobalt Blue as a background, put white text on it. The APCA lightness contrast is Lc 16 for black text and Lc -93 for white text.
Its perceptual complement is #694900, close to chocolate. Colors that look most similar are sapphire, denim, ultramarine. It looks fairly similar to people with red-green color blindness (ΔE 0), so its meaning mostly survives.