That's a good question. I had asked that question a while back, and no one had the answer. Don initially said that RF was what made the Cayenne, but I hadn't thought about asking about RF vs RC Fires, until later.
Also, he said the RF was what also made a Sunglow, vs just an Amel with little/no white borders.
But this was before it was really determined that RF and RC were separate genes. Back then, it was believed that RF and RC were the same, just called different names by different people.