A substrate marking apparatus for use in combination with a substrate comprising a multi-color change diacetylene compound is disclosed. The substrate marking apparatus comprises: at least two radiation sources operable to emit radiation of different wavelengths, optical transformation elements and a control system. The control system takes digital file information and converts this to a set of emission instructions for the radiation sources. The radiation sources are then applied to the substrate in sequence and intensity determined by the control system such that the substrate is activated to change from a colorless state to any one of a range of multiple permanent colors.