We demonstrate a new way to manipulate and to control the RGB chromaticity of the luminescence of Ln-based metal-organic frameworks with MOF-76 structure. This new way is based on preliminary UV photostimulation. Particularly, we reveal that besides the conventional ways to control luminescence chromaticity based on alteration of chemical composition and excitation wavelengths, the chromaticity of Ln-based MOF-76 can be strongly affected by the duration of preliminary UV photostimulation. This effect was demonstrated for the set of MOF-76 samples with different chemical composition: MOF – Y (100), MOF – Y/Eu (97/3), MOF – Eu (100), MOF – Tb/Eu (96/4), MOF – Y/Tb/Eu (87/10/3), MOF – Y/Tb/Eu (85/10/5), MOF – Y/Tb/Eu (80/17/3) (here numbers in the brackets denote the atomic percentages of the corresponding metal ions with respect to the total metal ion content). Remarkably, the effect of the alteration of initial luminescence chromaticity induced by UV photostimulation has been observed only for Y containing MOF-76 samples. The new UV-photostimulated luminescence chromaticity remains stable for at least ten days.