A method is disclosed for creating hydrogels with ordered crystalline structures that exhibit a characteristic colored opalescence. In addition to the unique optical properties, these materials contain a large amount of water in their crosslinked networks. The manufacturing processes include synthesizing monodispersed hydrogel nanoparticles containing specific reactive functional groups, self-assembly of these particles to form a crystalline structure, and subsequent crosslinking neighboring spheres to stabilize the entire network. Polymerizing a hydrogel monomeric composition around the crystalline structure can enhance the mechanical strength. The resulting network is dimensionally and thermodynamically stabile under various pH and temperature conditions. The color and volume of these crystalline hydrogel networks can reversibly change in response to external stimuli such as temperature, pH and other environmental conditions. These new materials may lead to a variety of technological and artistic applications, ranging from sensors, displays, controlled drug delivery devices, jewelry and decorative consumer products.