A new concept of mechano-responsive colour-change is introduced in the present work that allows for turning flexible materials into an optical mechano-sensitive sensor. For this purpose diffraction gratings based on laser-induced periodic surface structures (LIPSS) are produced on ductile stainless steel surfaces (X2CrNiMo17-12-2) using a femtosecond laser (fs-laser). When the material is deformed, the increase of the lattice spacing in the diffraction grating leads to a mechano-responsive change of the initial structural colour in the direction of longer wavelengths. With increasing plastic deformation of the metal, the formation of tilled and twisted slip bands leads to a disappearance of the structural colours before the material fails. Using metal masters, the LIPSS can be transferred to elastomers by replica casting. For elastomers produced by replica casting, the mechano-responsive colour change is reversible. The mechanically induced colour change of LIPSS is of particular interest for the development of novel switches, safety devices, strain gauges, sensors, hazard classification and early detection of material failure.