Reactive Blue 4 is a classic monochlorotriazine (MCT) reactive dye based on an anthraquinone chromophore. It is well-known for its reddish-blue shade and its effectiveness in low-temperature “cold brand” dyeing processes. It offers good solubility and reliable performance, making it an economical and versatile choice for achieving a range of blue and combination shades in various textile applications, particularly exhaust dyeing and printing.