The wild-type eye color in the fruit fly Drosophila melanogaster is dark red, as a result of a mixture of bright red and brown pigments. "Enzyme A" is encoded by the "a" gene, and is required to synthesize the bright red pigment. A lack of red pigment results in a somewhat brown eye color. You cross two fruit flies who are heterozygous for a recessive mutation that completely inactivates the "a" gene. What proportion of their offspring will have a recessive eye color phenotype?