Complementary colours are the hues produced when one of the three primary light colours-red, green, or blue-is subtracted from white light. The resulting colours-cyan, magenta, and yellow-are also known as secondary colours. In photography, printing, and design, complementary colours are used to create contrast, enhance visual appeal, and achieve balanced compositions. Understanding these relationships is essential for accurate colour reproduction, colour correction, and creating images with dynamic and harmonious colour interactions.