The late Frances Marshall of Ireland's Magic/Magic Inc. in Chicago suggested this very usable and practical expediency:
Black full-body Danskin (what they used to call a leotard when I was young). They come in a variety of styles (long sleeved, short sleeved, sleeveless, with skirt and without, and much, much more). Black is a total neutral, going with anything, so you can then make simple partial costumes to go over the Danskin: tunics, dresses, shortie jackets, body-hugging cloth emblem/shields, shorts, overshirts, etc. For more information on Danskins, go to: http://danskin.com/
For more information on the costume pieces that go over the danskin, go to: http://www.magicinc.net
and search the site for the book Supershow
by Frances Marshall.