Summary: The appropriateness of using silvering in Speyeria taxonomy was uncertain because it was not known if and how silvering is inherited. I found that offspring phenotype frequencies in strictly dimorphic S. mormonia from Manning Park, British Columbia suggested a single-locus, diallelic model for silvering, with complete dominance of the unsilvered over the silvered allele. Conversely, progeny that I raised from intermediately silvered S. egleis females from Mt. Ashland, Oregon displayed different degrees of silvering from one another and from their mothers. My results contradicted previous hypotheses that silvering is environmentally determined, that it is a maternal effect and that unsilvered morphs are maintained solely by mutation. Different dominance relationships, not differences in mate choice or heterozygote viability, account for differences between dimorphic and continuously-varying Speyeria populations.