The requirements are pretty minimal. You can use any fabric (as long as it's quality) and any pattern. Their one request (aside from the size), is that we use patriotic colors -- red, white, blue, gold. When I purchased the fabrics I was so focused on color that I completely missed the patterns. Until I started cutting. Lo and behold, I find korus even when I don't know they are there. Like this one, which I notice while cutting (look at the larger picture to see how easy it might have been for me to miss it).
And this one which I noticed while rearranging the pieces on a felt-board (you can see the edge of another fabric filling up the bottom left corner).
Sometimes it takes getting up close and personal to really notice what's right in front of you.