Real-time tuning of the emission characteristics of a dye encapsulated in a colloidal crystal through in-situ modification of the rejection wavelength is demonstrated. Mechanochromic tuning is used to modify the emission spectra of hydrogel-encapsulated crystalline colloidal arrays composed of electrostatically self-assembled monodisperse polystyrene particles coated with the photoluminescent dye Rhodamine-B, as shown in the Figure.