Midnight blue is a dark shade of blue named for its resemblance to the identifiably blue color of a moonlit night sky on or near the night of a full moon. Midnight blue is the color of a vat full of Indigo dye; therefore, midnight blue may also be considered a dark shade of indigo. Midnight blue is identifiably blue to the eye in sun-light or full-spectrum light, but can appear black under certain more limited spectrums sometimes found in artificial lighting (especially early 20th century incandescent). It is similar to navy, which is a also a dark blue.

There are two major shades of midnight blue - the X11 color and the Crayola color. This color was originally called midnight. The first recorded use of midnight as a color name in English was in 1915

The dark blue coats of US Army and US Marine Corps dress blue uniforms is called midnight blue. Midnight blue is an alternative to black as a color for dinner jackets. Due to the deepness of the color, midnight blue formal clothes are almost indistinguishable from black. This has been the case since the 1930s, when the Duke of Windsor popularized the color in suits and tuxedos.