Subject: Do all experiments absolutely need a controlled variable?

I don't really understand the concept of a CONTROL. I'm doing an 
experiment that tests the affect of different colored test papers on the 
test scores. I'll be testing pink and light blue paper to see if one is 
better than the other for easing test anxiety. But I have no idea what the 
control would be. I thought it would be white paper, but my teacher said 
that it isn't nessecary. I'll be using the Chapter Tests in a Biology 
class and one period will take the tests on pink paper and another period 
on light blue paper. Thanks for your help!

Re: Do all experiments absolutely need a controlled variable?