Pathogens shape the evolution of host immune systems and one gene family that experiences pathogen-mediated selection is the major histocompatibility complex (MHC), which encodes cell-surface receptors that present pathogen-derived antigens to T cells. The heterozygote advantage predicts that animals should select mates that are dissimilar or diverse in MHC genotype to maximize their offspring’s MHC diversity, which may confer greater immunocompetence. Parasite-mediated sexual selection further suggests that MHC genetic quality should be signaled by sexually selected traits. Female house finches (Haemorhous mexicanus) prefer males with redder plumage, which requires dietary carotenoids for pigmentation that are also used for general health (e.g., body condition and immunity). I hypothesized that redder plumage and better body condition would signal MHC class I genetic quality and predicted that plumage traits and body condition would correlate with MHC I diversity and genotype. I found that amino acid and supertype allelic diversity at MHC I did not explain plumage color or body condition, however, pairwise distance at MHC I between males correlated with pairwise distance in plumage saturation, suggesting a relationship between MHC I genotype and plumage color. This study will add to the growing field of honest signals of immunogenetic quality in ornamented birds.