A genetic marker for identifying transgenic Musca domestica by changes in eye color is described. The Drosophila melanogaster tryptophan oxygenase gene, vermilion (v), was tested for its ability to genetically complement the mutant tryptophan oxygenase gene in houseflies homozygous for green (ge). The v cDNA, placed under the control of the hsp82 promoter of D. pseudoobscura was transiently expressed in M. domestica embryos homozygous for the tryptophan oxygenase gene, ge, resulting in the rescue of adult eye color. The use of a gene from D. melanogaster to complement an eye color mutant in Musca provides the opportunity to develop a gene vector system for M. domestica and a select group of other non-drosophilid insects in which homologous mutations exist.