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About AB engine color.
https://theaviationist.com/2019/12/26/tu-22m3-backfire-engines-transition-from-idle-to-full-reheat-captured-in-stunning-detail/
[...]Second, the video shows with unprecedented detail the afterburner ignition sequence and the subsequent generation of the typical blue plume of many Russian engines (from 07:00 mark). In fact, as opposed to the orange plume you can observe on Western afterburners, Russian ones appear to be blue in color meaning that all the injected fuel is burnt before exiting the nozzle (the result of the engine design and the way fuel is dumped into the center of the cylinder): there is a more complete combustion and the reaction creates enough energy to excite and ionize gas molecules in the flame, leading to a blue flame appearance. In other words the blue flame is produced by molecular radicals, especially CH and C2, which emit most of their light in the blue region of the visible spectrum. The orange color is instead caused by fuel not completely burned out before exiting the nozzle, thus creating soot (unburnt carbon particles) that glows in the heat of the flame giving the orange color.[...]
https://theaviationist.com/2019/12/26/tu-22m3-backfire-engines-transition-from-idle-to-full-reheat-captured-in-stunning-detail/
[...]Second, the video shows with unprecedented detail the afterburner ignition sequence and the subsequent generation of the typical blue plume of many Russian engines (from 07:00 mark). In fact, as opposed to the orange plume you can observe on Western afterburners, Russian ones appear to be blue in color meaning that all the injected fuel is burnt before exiting the nozzle (the result of the engine design and the way fuel is dumped into the center of the cylinder): there is a more complete combustion and the reaction creates enough energy to excite and ionize gas molecules in the flame, leading to a blue flame appearance. In other words the blue flame is produced by molecular radicals, especially CH and C2, which emit most of their light in the blue region of the visible spectrum. The orange color is instead caused by fuel not completely burned out before exiting the nozzle, thus creating soot (unburnt carbon particles) that glows in the heat of the flame giving the orange color.[...]
