Last week I made some new cushion covers for my cushions in the couch. I used a yellow fabric I once picked up in a sale (designer unknown) and a black pattern fabric from Robert Kaufman.
The zippers I found in a second hand store ad since they are covered, it does not matter that their colour does not match the fabric. For the hidden zipper I used a great tutotrial by Sew, Mama, Sew.
On the yellow cushion I also added piping in the same fabric as the cushion cover. Here are some great tutorials on how to make your own piping cord: