Male secondary sexual traits purportedly facilitate female choice of a potential mate's quality. One example of male quality is the ability to resist detrimental infections by parasites; sexual traits that reflect parasite infection can allow females to select for parasite resistance in future offspring. High parasite numbers can constrain the exaggeration of male traits, but few studies have examined the effects of parasites on female secondary traits. Female Mexican boulder spiny lizards Sceloporus pyrocephalus, undergo a change in secondary sexual coloration over their breeding season and express red gular regions and gray gular stripes in association with late stages of follicle maturation during the reproductive cycle, as well as blue ventral stripes. We examined if color change associated with the female reproductive cycle varied in hue, saturation and brightness in relation to high nematode loads. Our results suggest that high nematode loads of particular areas of the body are correlated with dull, as opposed to bright, secondary sexual coloration in females of S. pyrocephalus. One reason females could be most vulnerable to nematodes during late reproductive stages is because of corresponding high concentrations of circulating testosterone known to occur in this species at this time. Testosterone has demonstrated immunosuppressive effects in many species; however, results have varied and conclusive evidence for its role in immune function remains controversial. Using a subset of individuals from this study, we found that high concentrations of plasma testosterone were significantly related to high nematode loads. These findings prompt further studies examining the physiological attributes of parasite infestation, the honest signaling capabilities of nematode loads and their potential role in sexual selection for coloration in females.