The flame morph is likely a polygenetic trait, which means that the phenotype (apperance) is an assemblance of multiple or many genes to create the flame look. This explains the high variability in offsping siblings, as variable amounts of the group of genes are passed on to each individual snake. As opposed to the single point, single gene (on/off switch) genes such as the recessive genes like albino and anerythristic that we are all familiar with and how it takes one copy of the gene from both parents (two copies of the gene in the offspring) to switch it "on", and either it has it or it doesn't. The fact that a flame can be bred to a normal and produce roughly half of the offspring with some degree of flame characteristic, says the the flame genes as a group have a dominant effect or are dominant in relation to the wild type color on the sides.
Hope this "sheds" some light and makes sense.
Jeff