I suspect the booster and sustainer engine jets are overexposing the camera. The main engine exhausts were also quite rich in flame on Atlas and Thor boosters. Those engines had film cooling- small holes drilled in the combustion chamber and nozzle coated the nozzle inside surface with raw kerosene (RP-1), that flowed along the nozzle to protect the nozzle from the flame. The main combustion used up most of the oxygen, so the kerosene did not burn in the nozzle area. But as soon as that unburned, but hot, fuel reached the outside air, it burned, surrounding the main jet with that envelope of flame. I saw a number of night launches of Atlas when I was stationed at Vandenberg in the sixties, and it lit up the whole countryside when it lifted off!