Federation Commander

x-tech looks more like the motion picture era of star trek, and the blue warp nacelles are usually fast ships. (though i have seen some of adam turner's fed heavy cruiser x ships with blue engine caps). X-Tech was ineffective in dreadnought size ships it had topped out in Heavy cruiser hulls. But all this is coming from someone who has never seen the x ship expansion so any more info from others would prolly be better

The art style for the X-ships is the least defined. Different artists have taken different tacks on it.

Regarding the naccelle-cap colors, in the "normal" (i.e. non-X) SFU these colors have pretty well settled out as typical (for Feds):
Orange ("as on tv") - all standard engines, including GW-era "hot warp" types (CA, DD, DN, DNG, NCL, NCA, etc.).
Blue - all "fast" engines (DDF, CF, CVF, NCF, DNL, etc.)

There is no standard for Klingons. Any glow is not "per tv" and is purely artistic discretion (and looks cool). Some folks have added a bit of a green glow around the "cooling tubes" (to look a bit like the Ktinga-class ship in ST-VI), but lots of other folks don't. I leave mine "glow-less" and just paint the cooling tubes silver, the "bulbs" at the back light gray, and add some silver and orange details (all per the old SL2200 ADB/TFG painting guides).

I for one definately agree things should be kept simple.

I have also followed the engine colours has djdood has stated for the feds the klingon ships i have to work on something that looks like a glow