Basic Dyes are cationic (positively charged) colorants that exhibit a strong affinity for substrates with a negative charge. They are the primary choice for dyeing synthetic acrylic fibers, modacrylics, and certain modified polyesters, where they form durable ionic bonds with anionic functional groups. Historically, they were also applied to natural fibers like jute, hemp, and silk using a tannin mordant, though this application has declined.

The standout feature of basic dyes is their unparalleled brilliance and high tinctorial strength—they produce the most intense, vivid shades achievable in textile chemistry. When applied to acrylics, they demonstrate excellent lightfastness and washfastness. However, on natural cellulosic fibers, their lightfastness is notoriously poor, and they exhibit a tendency to crock (rub off) and bleed unless carefully finished with specialized chemical fixing agents.