A series of dyeings was carried out with single dyes and two-and three-dye combinations on polyester and acrylic yarns and fabrics. Formulations were calculated based on reflectance factor values. Average deviations for both disperse and basic dye combinations are ± 7% in dye concentration under optimal conditions, and errors of up to ± 20% are possible. The inaccuracies are attributable to nonadditivity of the light absorption and to changes obtained on different substrates. The inac-curacies affect the first dyeing of the computed match and in most cases can be compensated for in correction calculation. -- AATA