Defined by wikipedia, a costume parade is: a test of the costumes against the final stage lighting so as not to produce a conflict in color differentiation in the final product. Also, costume pieces that restrict movement or fit strangely such as shoes, hats, gloves and so on may be added either in their final form or (usually) in rehearsal form approximating size, shape, etc. to allow actors to get used to them in advance.

One by one each boisterous, hilarious actor transforms into a character.  It's as if the sacred act of dressing in costume has literally given them a new skin and they assume the mannerisms of the men they are about to portray on stage. They become refined, their posture changes, their tone of voice slows and some are practicing different intonations. It is really fascinating to watch.  In the dressing room Costume Designer Alex Amini inspects the details of each costume with Director Danny Harvey.  They explain to me that they are trying to portray a sepia tone to reflect an era gone by.