I ordered a clear hard cover for my IPhone from Ebay a while ago. This cover is made for tuning and really wanted to use my washi tapes for this. In the photo below you can see what I needed.
First I picked out the washi tapes I wanted to use. I cut out a piece of paper in the sizes of the cover and covered it with the washi tapes. Then I just popped the paper inside the cover and then the phone. That’s it!