I haven't knit this pattern, but I can see why you're confused! I don't see when it says what yarn to use either. But I read through the pattern and judging by the yardage requirements, 3 sks of Cotton Perle @ 27 yds = 81 yds total, I think the Cotton Perle is just for the crocheted edges. If you look closely at the pics, you'll see they look different from the main part of the fabric.
Hope this helps!