Originally posted by Woolie Wool
The thrusters release a plume of plasma, not fire. Plasma can be almost any color depending on what material is being put into plasma state.
WARNING: technical nitpick
This is true for a cold plasma such as in neon lighting. However, for an engine or weapon we're much more likely to be talking about temperatures in the thousands or even millions Kelvin. Thermal emission is restricted to the following:
Most energy is IR (heat)
300 K (Kelvin, about 25 deg C, about 78 deg F) - IR, warm
>1000 K (about 700 deg C, about 1400 deg F) starts red - weak
>2000 K - more intense red. UV starts to appear
3000 K - orange-yellow
4000 K - bright yellow
5000 K - white - uniform over visible spectrum
higher T - starts to be blue
Obviously, this is insignificant next to aesthetics, but I do think red, orange, yellow, and blue-white are great engine colors aesthetically. Teal sucks.