An elastic, structurally colored fiber with reversible structural color is described in this article. Using an external magnetic field, Fe₃O₄@C superparamagnetic colloidal nanocrystal clusters (SCNCs) formed one-dimensional chain-like photonic crystal structures and were embedded in a polyacrylamide matrix. When the fiber was stretched/squeezed in the horizontal direction, the size of the fiber reduced/increased in the vertical direction. As a result, the distance between each sphere in chain-like structures can be reversibly changed through the elastic deformation of the matrix, and the structurally colored fiber displays brilliant colors, ranging from red to green as the mechanical strain changes, which can be clearly observed by the naked eye. The reflection peak can be tuned from 637 nm to 515 nm as a function of fiber extrusion or elongation. The novel structurally colored fiber is expected to have some important applications such as the substitution of some fiber-based wearable electronic strain sensors because this fiber does not require any additional devices to provide energy.