Through natural selection, nature has optimised highly complex systems, processes, and structures to achieve a broad range of functions. Materials produced in nature have evolved to efficiently perform functions such as structural support, signal transduction, actuation, sensing, light harvesting, charge transfer, self-assembly, and self-replication. Taking inspiration from natural design principles, architectures, and other heavily optimised features can provide a template for the design of biomimetic functional materials (responsive, autonomous, self-healing, etc.) for a variety of uses. In the same light, photonic structures in nature have been fine-tuned for over 520 million years to yield a remarkable array of hierarchical micro- and nanostructures for various light-matter interactions. In this regard, cephalopods (squid, octopus, and cuttlefish) have mastered the ability to rapidly and precisely tune their dermal colouration, patterning, and texture for both camouflage and signalling. This neurochemically-modulated ability allows for unparalleled adaptive camouflage through a complex, layered system of optically-active, proteinaceous nanostructures (collectively known as chromophores) which reflect, filter, and scatter incident light. Since the discovery of the highly-reflective, self-assembling protein known as reflectins - the active component of chromophores - many have taken to exploiting these proteins for the fabrication of optically-active materials. In this context, this thesis describes the utilisation of synthetic biology approaches, synthetic and analytical chemistry techniques, and materials fabrication and characterisation methods to investigate reflectin properties, design, fabricate, and characterise reflectin-based materials, and develop novel materials exploiting reflectin properties. The angle-dependent optical properties of several reflectin thin-films were characterised over the UV-Vis-NIR region, with previously unreported angle-dependent reflectance properties revealed. Through the design and fabrication of a bio-inspired multilayer reflector, this angle-dependence was subsequently modulated while conserving single-layer optical properties. The design, fabrication, and characterisation of a novel method to control the optical properties of reflectin-based thin-films was then described; photo-induced isomerism. Following this, we report our investigations into the optical properties of cellulose nanocrystal films, the integration of reflectins into these materials, and the characterisation of reflectin/cellulose humidity-responsive materials. We describe the characterisation of full-length reflectin assembly properties alongside its corresponding N-terminal motif, and our efforts to modulate reflectin hydrophobicity via post-translational modification and post-fabrication hydrophobic-treatment. Finally, due to their relatively high proton conductivity, we investigate reflectins as a potential platform for neural tissue engineering, revealing how covalent functionalization with native reflectin enhances proton/ion conduction, promotes enhanced metabolic activity and proliferation, and supports differentiation of analogue neuronal NG108-15 cells. Together, these findings may represent a key step towards the development of the next-generation of reflectin-based materials. Further investigating the design space, including thin-film structure and morphology, thickness and bilayer interactions, concentration and formulation, and methods of fabrication will facilitate the development of the next-generation of advanced optical materials for adaptive colouration.