Go to:
www.goosystems.com

They have specially formatted paint that allows you to paint any wall and turn it into a projection screen. It's really cool and got good reviews from TechTV. It is a little pricey but cheaper than buying an actual screen.

Interesting site - they even have paint for rear projection which is something that I'm interested in.

Do you think that some acrylic latex of the correct shade would make a good approximation?

wow,
looks like some nice stuff but it can also get a bit pricey. would not be happy if i chose the wrong color or didnt apply it just so. cant return it or sell it if your not happy once you applied it to your wall.

Check out what I have been learning and doing with DIY screens and paints here