So looking at these screenshots at work, I came to the realization that the near-black areas could be seen just fine on this crappy, uncalibrated monitor.
I'll have to check when I get home to see if my monitor is properly calibrated, but I feel it's probably closer than this one. I've adjusted the screenshots to look like what they looked like on my monitor on this one.
In the first screenshot, it's almost impossible to tell where the metal ends and the sky starts.
In the second screenshot, the metal wall looked almost completely black, and you couldn't easily tell where the wall ended and the floor and ceiling started.
You should attempt to calibrate your monitor and/or game to match sRGB as closely as possible. That's what Paintball2 is designed for. Also keep in mind that some people will have monitors that are darker than sRGB, so you might want to try cranking down your gamma and playing the map.
As for the -scale parameter, that goes in the lighting process. The easiest way to do this would be to find the .bat file you're using to compile (probably one of the final compile ones), make a copy of it, then on the rad line, (where it has -extra -chop, etc.), add -scale 2. Then compile your map using the copy batch file.