A Border for the Optical Illusion Zig Zag Blanket

I'm about two thirds of the way through the blanket, and have started thinking about a border for it. 

The blanket started in purple with a foundation chain, and then two rows of double crochet (American terms being used). I'll apply a border on the other three sides of two rows of double crochet. The top one will be made first, and then the sides. There might also be a single crochet too. I'm not quite sure yet. As the rest of the blanket has been made by working into the loop, I'll do that too on the edging.

Then, switching to the light blue, I'll make a double crochet and a chain into every other stitch. This will be done through both loops. Changing to teal, the next round will be working two doubles into each hole created by the chain stitches in the round below. A further round of double crochet will be added, working only into the back loop.