O/E: A localized uniformly black area on the heel of the right foot.
Here is the dermatoscopic image.
This is most likely black heel aka "talon noir." The dermatoscopic photo was taken after paring down the keratin and shows black globules. I should have applied some peroxide to dissolve the hemoglobin. Will ask the patient to do so.
Foreign body secondary to astroturf has not been reported, and this looks like black heel. There are no good dermatoscopic images on PubMed.