In versions prior to VX.2 the changes are stored in mgc_nse_2007.ini in C:\Users\<user_name>
To set it choose File > Preferences > Appearance > Symbol Window > Page Color and pick your color from the color chip gadget.
In VX.2 and newer the symbol editor inherits settings from DxDesigner, if you have an orange background in Dx you should have an orange background in the symbol editor. The same for black or white.
To set it choose Setup > Settings > Display > Objects > Background and pick your color from the color chip gadget, or use Load Scheme and load a predefined color scheme.
Thanks Shannon. I'm able to change the page color once I have the symbol editor open, but I can't save my preferred settings to be default. I can see the mgc_nse_2007.ini file with the settings and would edit that directly, but I don't know the proper commands or syntax.