If you see them in person, you'll notice that fires have a very light coloration, flames around the sides (usually), AND they are also the heterozygous form of a trait that is a BLACK eyed leucistic (often with some yellow discoloration) in the homozygous form.
They make for a great addition to combo morphs, and really cause colors to pop. Fireflies (pastel fire) are a great example, just compare them to regular pastels and you'll see what I mean about colors being more well defined.