A host-guest based colorant was synthesized by intercalating indigo molecules into the nanochannels of zeolite L (ZL). Reductive washing thereby ensured the efficient and selective removal of non-intercalated indigo molecules. The UV-vis diffuse reflectance spectrum of the product after intercalation and reductive washing (designated as indigo-ZL) was found to resemble the solution spectrum of indigo, leading to the conclusion that the formation of indigo aggregates is prevented due to the steric constraints imposed by the microporous structure of ZL. The application of indigo-ZL on cotton was tested by roll coating. The light absorption properties of the resulting textile prints showed no significant alteration when compared to the pure indigo-ZL powder. The UV-vis diffuse reflectance spectra of mixtures consisting of indigo-ZL and a further ZL-based colorant were successfully predicted by the weighted addition of the respective primary spectra
