This is actually normal, and expected. The issue with these specific Starship tests is that the flight plan calls for 1) a height of ~10 km, 2) not going supersonic. The second one is quite critical, because supersonic flight introduces much greater stresses on the craft.
Given these two limitations, Starship currently carries very little fuel. Think of it like a mostly empty soda can with a few sips sloshing about the bottom. Adding 3 Raptor engines to such a tank makes them way too powerful to run at 100% thrust the whole time.
On the launchpad, all 3 Raptors start off at full thrust until well clear of the pad. At that point, one engine at a time starts throttling down gradually, so as not to go supersonic or exceed the 10 km flight plan. A throttled engine does not burn as cleanly or efficiently, which is what results in the orange exhaust plume. Same as your campfire, blue flame is hotter than orange/red flame, and the bluer exhaust engine is therefore burning hotter and providing more thrust.
As Starship gets closer to the 10 km peak, it shuts off one engine at a time, and finally throttles the final Raptor down as low as it can go. Note that Raptor engines have a minimum throttle that is ~20% of max thrust, below which the only option is to shut down.
Given these two limitations, Starship currently carries very little fuel. Think of it like a mostly empty soda can with a few sips sloshing about the bottom. Adding 3 Raptor engines to such a tank makes them way too powerful to run at 100% thrust the whole time.
On the launchpad, all 3 Raptors start off at full thrust until well clear of the pad. At that point, one engine at a time starts throttling down gradually, so as not to go supersonic or exceed the 10 km flight plan. A throttled engine does not burn as cleanly or efficiently, which is what results in the orange exhaust plume. Same as your campfire, blue flame is hotter than orange/red flame, and the bluer exhaust engine is therefore burning hotter and providing more thrust.
As Starship gets closer to the 10 km peak, it shuts off one engine at a time, and finally throttles the final Raptor down as low as it can go. Note that Raptor engines have a minimum throttle that is ~20% of max thrust, below which the only option is to shut down.