Besides for the Uncle and his niece, all the actors wore dull earthy colors throughout the play.  This may have signified the poverty in which they all lived, or perhaps the boring lives they all led.

The uncle, with his purple coat, and the niece, with her orange outfits, may have been wearing colorful clothing to emphasize the comedic purpose that their characters serve.

Madame Raquin wears black during the entire play.  This may symbolize her constant mourning for her son.  By always acting as though her son is sick, she doesn’t allow him to ever really live.

Camille has minor costume changes such as the addition of a scarf and jacket.  These show his emotions towards ideas.  He lives life on the surface and never really discovers the bigger picture of things.

During Therese’s wedding, Madame Raquin dresses her up with a veil and ribbon.  The fact that Madame Raquin dresses puts on the outfit shows Therese’s passivity in her wedding.  Also, the fact that she doesn’t have a significant costume change shows how nothing has changed for her.