A colour developer is a specialized photographic chemical used in colour film and paper processing. It not only reduces exposed silver halides to form black metallic silver but also produces oxidation byproducts that react with colour couplers to generate specific dyes. This dual action enables the formation of accurate colour images with proper hue, saturation, and tonal balance. Colour developers are an essential part of colour photographic processing, ensuring consistent, high-quality results in both film and darkroom printing.