The remarkable, vapor-induced transformation of the yellow polymorphs of [(C6H11NC)(2)Au-I](AsF6) and [(C6H11NC)(2)Au-I](PF6) into the colorless forms are reported along with related studies of the crystallization of these polymorphs. Although the interconversion of these polymorphs is produced by vapor exposure, molecules of the vapor are not incorporated into the crystals. Thus, our observations may have broad implications regarding the formation and persistence of other crystal polymorphs where issues of stability and reproducibility of formation exist. Crystallographic studies show that the colorless polymorphs, which display blue luminescence, are isostructural and consist of linear chains of gold(I) cations that self-associate through aurophilic interactions. Significantly, the yellow polymorph of [(C6H11NC)(2)Au-I](AsF6) is not isostructural with the yellow polymorph of [(C6H11NC)(2)Au-I](PF6). Both yellow polymorphs exhibit green emission and have the gold cations arranged into somewhat bent chains with significantly closer Au center dot center dot center dot Au separations than are seen in the colorless counterparts. Luminescence differences in these polymorphs clearly enhance the ability to detect and monitor their phase stability.