just posted something in the other thread
An Even Cheaper Possible Alternative to Hi-Power screens
use a satin or satin-like white fabric (highly reflective) and line the back with black cardboard.
colors were richer, blacks were deeper, and contrast was intensified.
if you have a rainbow problem you will notice it more with this, but at under $30 for the raw materials, most everybody can afford to give it a shot.
look in the thread in the dlp forum for a little more detailed account.