I don't know about if the tempura is good or not..seems to me it is powdercoating paint. It requires heat. I have a jar of really cool green that I bought from a clothing place and it is a heat activated dye, and I tried it and it did work but also did not. It turned the plastic green but it also had a dirty look and feel to it, it was quite strange. It was like the pen had dust on it and no matter how hard I tried I couldn't get it to go away, but it wasn't dust of course. I could be wrong on your product though..maybe it works.
This place though, all there stuff works, and they have some cool things..I buy a few things from them now and again..just sucks they are in PA and so they have to charge taxes.
http://www.smooth-on.com/