The usual preservation of these plant fossils (cycads, cycadeoids, ferns, etc.) from the Sanford area of NC is a brown or reddish-brown impression on matrix.  But there is also a silver-grey impression on matrix that's an interesting variation.  This area was a swampy lake during the late Triassic.  It was one of many rift valley lakes along the eastern seaboard that formed as North America and Europe broke apart and the Atlantic Ocean came into existence.