Doog,
I used the exact same lighting for both shots. The only difference is that I recalibrated the white balance for the white background vs. the blue, but even that didn't make an appreciable difference. I didn't do any editing or adjustment in Photoshop or other software. I don't use a flash, just positionable lighting.
On my monitor the white background picture is indeed darker, which is one of the reasons I don't use the white background, even for the tri-tone scheme. The blue background is actually more representative of what the actual model looks like while the white background shows everything darker and would require editing to get it back to a "representative" state. The only thing the white background shows better, ironically, is the weathering on the decals/markings...but then I expect that because they are predominantly white and the camera will "see" that clearer with a white overall background. It's a small trade-off but one I normally accept as it's very small in the grand scheme of things.
One of the other reasons I don't use the white background is that the camera picks up the detail better, IMHO, with the blue background. Notice, for instance, the detail level on the gun muzzle flash in the blue vs. the white. I can't really explain why, but my camera prefers the blue background and produces better photos as a result. This is true whether the photo is a WIP or a finished one.
I will say that at first-glance, the white background does produce a more "truer" impression to the eye...but when I placed the model on my desk and compared it to what was on the monitor, it wasn't as "real" vs. the blue if that makes any sense.