I’m a textile dyer and, with over 30 years’ experience in the industry I’ve seen a few things come and go in terms of the ‘next big thing’ but the fundamentals of how dyes remain intact and attached (or not) to fibres hasn’t changed one bit.
Some dyes sit within or on a fibre, tenuously clinging on for dear life via weak gravity-like forces and become detached as soon as they see water in the form of sweat, rain or a washing machine. They can be made insoluble by the use of chemical after-fixes (or mordants) which makes them less prone to being washed off although they can still be rubbed off onto your underwear, sofa or car upholstery.
Some dyes have positive or negative electrical charges that are attracted to opposite charges within and on fibres and this attraction can be quite strong, making the dye difficult to remove (for instance basic dyes on acrylic or acid dyes on nylon).
