Just spent an afternoon applying decals to crockery to go with a couple of my collections. It was a very enjoyable process and I was completely absorbed in it. The transfer paper is blue until it is fired, then it becomes clear, but in fact I like the blue blocks, and if I was doing it again I would have included some blocks of colour in the designs. 
The paper comes from Fotoceramics - send them your designs and they will print them off for you.