A wide variety of products providing colour to leather and paper are often imprecisely categorized. A correct classification contributes to a better understanding of the their features and is therefore useful both in the recognition in the materials eligible for conservation, as well as in the application of dyes and colourstuff for a proper in-paint and retouch. The dyes and colorants will be discussed according to the most common classifications: pigment based or not, natural/synthetic and, above all, their substantivity: direct, ionic, reactive and complex.