Intrinsic transparent conductors (ITCs) correspond to a unique class of TCs that do not need intentional doping. This character can provide ITCs significant advantages by avoiding severe "doping bottlenecks" and dopant scattering usually encountered in conventional transparent conducting oxides (TCOs). However, the realization of ITCs generally requires the minimization of photon absorption and reflection in metallic conductors, which is difficult due to the gapless nature of their band structures. Here, based on first-principles calculations, we illustrate a feasible strategy to design optical transparency in metallic conductors by a synergetic effect of symmetry and spatial-distribution forbidden transitions between their energy bands around the Fermi level. The validity of this design strategy is demonstrated in a zero-dimensional electride, K_{4}Al_{3}(SiO_{4})_{3}, which exhibits both electrical conductivity and optical transparency in the ultraviolet spectrum. More interestingly, we find that this transmittance range can be tuned to the visible spectrum region by chemical substitutions in K_{4}Al_{3}(SiO_{4})_{3} with the elements that have either larger electronegativity or smaller atomic radius. By examining dozens of possible cation substitutions via high-throughput calculations, we identify several promising candidates that have the potential as ITCs.