if you have a barnes n noble book store near you, get a motorbooks / workshop book called how to paint flames or another one called how to custom paint your car.
They only run about 20 ea. I look thru mine constantly. Lots of good tips in there. In the flames one, is a small chapter with mike lavallee. He is doing blue flames. But in the other book, there's a chapter on tradional colors.
There are many styles of 'real' flames. I had started going in one direction only then went in another direction, using templates. Seems to have gotten alot of attention in my town.
the trick is layers of colors, the above formula is a good start.
When using a template, just remember to use only bits of it, random areas, or it will look stenciled.
Ex~ french curve, don't use the whole side of the curve, just a lil on the bottom curve here, and then a lil on the opposite end there. To start out, just make your own template in thick posterboard, it's cheap. Make different sizes, they don't have to be perfect either just as long as the edges are smooth.
look at alot of pics for references. I print them and tape them around the back so I can look alot.
main thing is have fun, practice practice!