I wanted to say you could not simply tell by the coloration of exhaust pipe if mixture was lean or rich ,as other factors will also have a big influence on coloration ..:time exposed to the conditions,ignition timing ,wall thickness,coating inside the tube,airflow around the pipe etc..all things you will not be able to quantify when looking at a pic.You will be able to see the oxidation only-imagine the exhaust in an inert chamber would show no coloration at all...as an extreme example.
The things you mentioned:
time exposed to the conditions, ignition timing ,wall thickness,coating inside the tube,airflow around the pipe etc..
I think they have just a very small impact on temperature but not big enough to change the colour in such a extreme way. Furthermore for some its just a matter of time until your top surface of the exhaust reaches its temperature.
Straw made a good point here.
Lean and rich mixture affects the temperature in a big fashion. The things you mentioned do not.
Nevertheless I think the main difference in this case is the material. The Ferrari maybe has more chrome in the steel or anything else is different. I don’t know enough about material to say anything for sure but I have seen hot metal already. For some you would not even see a big difference but luckly you feel the heat. Its the only thing that stops you from touch it.
You can see that the RB one has similar colours on some spots. Its just harder to see because of the general darker appearance.