Blue is one of the three primary colours in the RGB (additive) colour model, as well as in the RYB colour model. It lies between violet and cyan on the spectrum of visible light. The term blue generally describes colours perceived by humans observing light with a dominant wavelength that's between approximately 450 and 495 nanometres. The clear daytime sky and the deep sea appear blue because of an optical effect known as Rayleigh scattering. An optical effect called the Tyndall effect explains blue eyes. Distant objects appear more blue because of another optical effect called aerial perspective.

Matt may refer to:

• Matt (name), people with the given name Matt or Matthew, meaning "gift from God", or the surname Matt
• In British English, of a surface: having a non-glossy finish, see gloss
• Matt, Switzerland, a municipality
• "Matt", the cartoon by Matt Pritchett in the UK Telegraph newspapers
• MATT, gay male erotic artist