Generally, a synthetic smart material exhibits a monotonic response behavior. Its material property shifts reversibly between two equilibrium states upon switching a pair of reverse external stimuli. This paper reports that a solvent-swollen elastomeric film turns opaque and then autonomously reverts to transparency through a single trigger of exchanging the swelling solvent with a poorer solvent. We demonstrate this method capable of recording optical information with a regulatable lifespan into the soft material, which is reminiscent of the memory in the brain. The intriguing non-monotonic response behavior is proved to arise from the fast molecular mixing of solvents during solvent exchange, which pushes the system far from its swelling equilibrium. As a result, excess solvent molecules separate into a new phase and are temporally trapped within the gel film, creating an off-equilibrium heterogeneous structure that scatters light. The heterogenous structure later autonomously vanishes, as the excess network elasticity relative to swelling equilibrium drives the excess solvent molecules out of the gel film. By adjusting the solvation ability of the poorer solvent, the lifespan of off-equilibrium structure can be continuously regulated from mere hours to several months.