Bob,
As you know real fire is normally airbrushed over black, but I have seen it before over lighter bases. I remember seeing it over a silver before and it looked pretty good. This was quite some time ago, but if I remember right, they basically used a over-reduced black to create a smoke effect as the backdrop. It had some transparent holes/gaps in it. So this would be your 'black' background for your candy real fire. The black smoke was quite a bit larger than the real fire area. I guess the main thing you need to watch using the black over the white and using this effect would be to make sure it doesn't turn into a black blob. Make the edges quite a bit thinner and have some whispering smoke coming off the top and the sides.
Hope it works out for you.
Like to see pics of it when you are done
:luck: