A method, i.e., trapping of structural coloration (TOSC), for fabricating solid 3D network-structured photonic crystals featuring tunable visible structural colorations includes the steps: a PS-PVP copolymer is dissolved in a chloride-containing solvent and is cast as an initial film, the copolymer self-assembles into 3D periodic network-structured morphology; the copolymer in the initial film is swollen in a polar solvent to form a solvated film; the solvated film is dried to form a solid photonic crystal. During evaporation of the polar solvent, the PVP blocks of the copolymer become glassy and form a thin glassy layer on the surface of the solvated film such that the 3D network structures of the copolymer in solvated state can be preserved into the solid photonic crystal revealing the similar periodicity and dimension to that in solvated state, which is very distinct from the film having 1D lamellar structure.