I discovered that some of my colour pens could "erase" certain other colour pens I have due to their alcohol content or some such... Experimenting with this technique I laid down some rough purple as a background and drew the joker in black marker. After filling his hair with green I set about adding the highlight areas (including eyes and teeth) with a yellow pen which enabled the "erasure" technique. Came up alright I reckon
It's a cool technique and one used very effectively here. I haven't used markers in ages but I always thought they were fun although more fun when you're using 'em!