Colourful plumage ornaments may evolve because they play a role in mate choice or in intrasexual competition, acting as signals of species identity or of individual quality. The zebra finch (Taeniopygia guttata) is a model organism for the study of mate choice and its colourful plumage ornaments are thought to be used in both of these contexts. Numerous genetic colour variants have been described for this species, but they are rare in the wild. This raises the question whether discrimination against deviant phenotypes maintains the species’ uniform plumage colour (rare mate disadvantage). Further, comparison to closely related species suggests that the lack of colourful ornaments in female zebra finches is a derived condition. Male preferences for less ornamented females may have led to sexual dichromatism in the zebra finch. Here, we test the role of plumage ornaments experimentally by altering male and female colouration to mimic two types of naturally occurring genetic colour variants. We estimated effects on social dominance and reproductive success in large breeding aviaries in one domesticated and two recently wild-derived populations. Hypotheses, methods and analyses were preregistered to ensure maximal objectivity of the results presented. Despite a fairly drastic manipulation and a powerful experimental design, we found no effect of the treatment on social dominance or on reproductive success. Our results suggest that mate choice is not the mechanism that maintains homogeneity of zebra finch plumage colouration, or that can explain the loss of ornaments in females.