Appearing as an ordinary black or gray bird when light hits a full grown adult male is obvious how they get their name. The black areas become brilliant deep purple in color.

It take a male 3 years to reach adulthood and acquire their plumage. Male martins molt in to their purple plumage during their second Wintering season in Brazil.

Until a male martins second season molt they are often confused to be a mature female. Males seem to have darker heads than their female counterparts.

Sub adult male martin have a darker head & back and lighter under parts. Gray on the forehead and often have a few dark feathers showing on the breast

Females tend to have more purple on their crown and nape, (shoulders), back and rump than young females.

Molt starts in late summer and stops during migration then resumes at winter roost where plumage change occurs.