From pattern:

“Picking out the yarn for this blanket is as much fun as knitting it. It’s a great opportunity to play with color and texture without regard to gauge. In other words, there are no rules and no limitations - you can use any yarn you want. We like to bebin by picking a color scheme, green in this case. We pull out every green yarn in the store and make a huge pile on the floor. You should do the same. Pick a color and then walk around your yarn shop gathering different yarns (your local yarn shop owner will love the mess this makes!)”