I don't have any xanths to show you but with my smaller Jackson's it's more about posture than coloring. Females go a bit dark either way. Receptive females stand there like deer in headlights and unreceptive rock back and forth and hiss or gape.
Had a female do that to a leaf that had a bamboo stick coming out behind it. Not sure why, but I had a feeling she thought the male had gotten into her enclosure one day I was feeding and I had to remove the stick to get her to stop swaying with her mouth open.