I may have posted about this before. But I have noticed at night time when its cool and damp outside, when I vtec and a car is behind me with their headlights shining I can see MAD smoke coming out from the back of the car. But its ONLY if there is a car behind me and if its cool and damp out, any other condition and there is no smoke. It doesnt appear to have any color, and it seems to only smoke above 7k rpms. I loose about 1/2 qt. of Mobil Syn. every 3k miles, maybe slightly more than 1/2 qt. I also noticeblack soot on my bumper regularly. Compression check and down check in order? Possible bent valve maybe?

 

If it were daylight, you'd probably notice that the smoke is black in color. Sounds like you're running rich. I'm not going to dissuade you from checking compression, etc... but I'd guess it's just the ECU pumping in unnecessary fuel. If your plugs are old, you might replace them to make sure you're getting good spark. If your air filter is old, you might replace it to make sure you're getting enough air to burn all the fuel. Otherwise, I'd say it's probably just normal. The light from the car behind you just accentuates the cloud behind you.
FWIW... I never noticed this when I had my VAFC installed (which leaned out the mixture up top), but as soon as I took it off, I noticed the same things that you are seeing immediately.

 

My thoughts. First, the black soot is normal, the engine runs rich at high rpms to cool the engine. buring 1/2 quart per 3k miles is normal in my car.

Are you sure it isn't air condensation? I'd ask a friend to be the car behind you and smell what kind of 'smoke' it is. Your car, and its problems if any, don't care if it is night or day out. The dewpoint is lower at night though so that could be a clue.