The flame is light blue with that diamond shaped white thing.
Shock diamond.
Frontier engines rather resemble RS-25
Not anymore they don't. The old ones did. The 1.5 frontier III engine itself looks and acts nothing like RS-25s except the flame is the same.
It's like I said, you can go into the weeds about fuel and flame colours but SFS doesn't support RP-1 or LH2 or methane or solid fuels. You get SFS fuel and 5 different engines. You pick whichever one will lift the stage and payload and if that matches the real thing then that's great.
So although it's not
identical to the RL-10s on the Exploration stage of SFS, if you were to use any other engine (kolibri would be the closest in size and thrust) to push that stage + a payload (which is going to be over 100tons all up hopefully), then it wouldn't make orbit because it doesn't have the thrust. Even with 4 of them, which is what you're supposed to have.
I know it's not. I said it has the
interstage that is between the core and the Exploration upper stage on SLS, not that Mars Pathfinders as yet un-named rocket has an exact replica of the Exploration upper stage.