Like the Quirky B's when starting out, one takes baby steps. I don't have a photo of the original keyboard but I recall sitting at the kitchen table and dabbing flat black Tremclad paint onto the border around the keys. I think I painted the sides of the keys black, too. It was painstaking. And then I painted a bit of nail polish on the top of each key. I don't think that the letters were obscured. It was a babyish, hack-of-a-job.
So the skulls started out pedestrian but every day I work on another, they become more sophisticated. With a good two months of scary skulls available in stores up to Halloween and then the aftermath, the experiment has time to take.
Click on any of these photos to enlarge and see the detail.