Is there any way to change the default preview render background color from black to anything else?
Yes, on your plugin folder there should be 3-4 pics named background, in order to change the background; you must replace these files with the color or image that you want and name them as the original ones, also, you should resize the pictures according to the original ones. I recommend you to simply move the original background pictures to another folder and don't delete them, because you might gonna switch back to the default.
I hope this helps, Alan
It doesn't. The process you described is to change the city background in game, which is not what I want. I'm trying to change Gmax's default render background color.