The debate over whether the Disney ships’ hulls are painted black or blue has been going on for years and continues today. The mystery of the black paint was revealed in a 1998 book dedicated to the Disney Magic.
Traditionally, classic ship hulls were painted black. It was determined that black was too sinister and too depressing for a Disney ship. In order, to keep the visual look of a classic ocean liner Disney settled on a color that is 87% Black and 13% Blue. This unique mix can cause the ship to visually change colors, depending on a number of factors including the weather, time of day, the light, and even your perspective to the ship.
Here is some visual proof to help end the mystery.
Compare the blue paint on the porthole to how the ship looks black at night.
At the end of the day if you call it blue you are only 13% correct. The ultimate goal for Imagineering was to get that classic ocean liner look while still keeping to the Mickey Mouse color theme. The color is intended to be black with just enough blue to give that magical quality of color changing depending on the weather, time of day, light and your perspective of the ship. The name for this color has often been referred to as Monica Blue.