"or a pearly coat"
'Pearlies' collecting for charity
Creative Commons Attribution Share Alike'Pearlies' collecting for charity - Credit: Garry Knight, Flickr

A pearly coat was originally a coat decorated with mother-of-pearl buttons.

In 19th Century London, costermongers (vendors of produce from barrows or carts) used to sew mother-of-pearl buttons onto their clothes. This tradition was taken up by a young orphan, Henry Croft, who started a trend of wearing pearl-decorated clothing while collecting for charity. This theme was developed by the Pearly Kings and Queens (or Pearlies), a charitable organisation whose Kings and Queens wear elaborately-decorated costumes, although the original mother-of-pearl buttons have been replaced by plastic ones.