Nanoporous materials, such as metal–organic frameworks (MOFs), enable the separation of various molecular mixtures. Thus, detailed knowledge of multi-component diffusion properties of the guest molecules in the pores is vital. Here, UV/Vis absorption spectroscopy combined with step-by-step-synthesized MOF films with high transparency are used to measure the multi-component dye uptake and diffusion in a straightforward fashion. The time-resolved single-component, binary- and ternary-mixture uptakes of methylene blue (MB), nuclear fast red (NFR) and acid yellow 17 (AY) by MOF films of type HKUST-1 from ethanolic solutions with low dye concentrations were investigated. It was found that the diffusion of MB is approximately one order of magnitude slower than the diffusion of NFR or AY, independent of whether it is a single-component uptake or a mixture uptake.