Yes, the interior of the flame is hotter, so it should be a lighter color.
Laszlo (sp?) has a fantastic article on how to paint at his site,
Hot Lead. I\'d link to the specific article, but it looks like his site is over the bandwidth limit for his server, so it\'s not available at the time of my post. Whenever it\'s back online, you should be able to find the tutorial on there pretty easily.
But, for some examples, check out the following images here on CMoN:
44292
35671
23912
10159
2608 (Laszlo!)
686
And, in my opinion, one of the most stunning pieces: 3369.