Instead of buying expensive buckets of Rosco chroma key paint for $60 per gallon you can have a hardware store mix up a bucket by giving them the correct PANTONE code for the color you want. Just give them PANTONE 2735 for a blue screen or PANTONE 354 for a green screen. You could also find similar colored fabric from Wal Mart and use that instead of an actual painted wall.

Though it really doesn’t matter getting it that close to the Pantone colors, here’s other info for getting paint mixed

Green screen: PANTONE 354 =
C: 95%
M: 0%
Y: 100%
K: 0%

Blue Screen: PANTONE 2735 =
C: 99%
M: 100%
Y: 6%
K: 7%

If the place you get paint mixed doesn’t have the capability of using any of these codes then just print a swatch out of them on a CMYK color printer

And remember to light your wall separately from your subject, and light it well!