A monochrome outfit is one in a single colour, worn head to toe. In this example from over 50s blog Is This Mutton? the outfit is burgundy separates with boots and a hat.
A woman stands in a lush garden, wearing a burgundy outfit, including a skirt and hat, with a smile on her face.
A woman stands in a lush garden, wearing a burgundy outfit, including a skirt and hat, with a smile on her face.