Subject: How do the game peices that you sometimes see on cereal boxes work ?

How do the game peices that you sometimes see on ceral boxes work? (the 
game peices that you have to use red cellophane to read)
I know about the diffrent rays of color and how some don't get through the 
red cellophane, but how do they make the game peices? I've tried and tried 
but I can't seem to get it right. we've already moved on to the next 
chapter in our book, but this is still bothering me. Thanks for all your 
help!
  student@cghs

Re: How do the game peices that you sometimes see on cereal boxes work ?