Ah, I belong to the club of unexpected final results too! I think that you have just invented a new pattern, a rather refined and quiet one, so I would treat it as if the result was intentional. I definitely wouldn't zigzag around the block in red. I'm figuring that you are not referring to free motion quilting? If you don't free motion quilt, I suggest using a green thread to match your dominant colour and using a walking foot to quilt diagonally across the whole quilt in both directions, forming diamond shapes. I guess you could use your zigzag stitch or a sewn-out zigzag stitch for that.