I didn't want to put in scientific explanations for colors, because I have caught flak on the board for getting "too grounded in reality" previously, but since other people are, I'll jump off the cliff as well.
Orange flames occur when oxygen burns with something, carbon (I think), and is the coolest of the flames (temperature wise)
Blue flames will naturally occur when oxygen burns with hydrogen (look at the space shuttle's main engine - not the boosters - flame), oxygen+acetyline - welding torches, but they're not used in space propulsion, oxygen+propane, etc. Blue flames are hot flames.
While green and purple flames are possible, they're unlikely to occur, and if they do, it'll be faint. Sometimes the flames from jet afterburners look purple because blue light from the hotspot'll be filtered by orange flame (or the other way around). The SR-71 has a green flame for its prestart sequence (it requires a triethylborane explosion to get the fuel to ignite), but its contrails are generally blue and orange.
You could use stars as your models for glow colors. My reasoning behind that is that since ships use something high-tech like fusion engines, and stars undergo nuclear fusion, so the colors would possibly be similar. We haven't discovered any stars that glow green or purple, but the red->yellow and blue->white spectrum colors are common.
As for glows in Override, I'll bet that you've never noticed it, but all the UE capital ships have thin yellow glows in the back.
Matrix
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"Nothing is fool-proof to a sufficiently talented fool."
