The background cannot be changed ( for now ) but the client for OA085 already comes with a console which can be configured in size, transparency and color since I've contributed myself to this (
http://openarena.ws/board/index.php?topic=3095.msg28529#msg28529 ) ; try playing a bit with those cvars :
- cl_consoleType : 2 for new console color/transparency behaviour , old console with every other value
- cl_consoleHeight -> its value can be between 0.1 and 1.0 ( 1.0 for full screen console )
- cl_consoleColorAlpha ( transparency ) "0 - 1.0"
- cl_consoleColorRed (red gradient) "0 - 1.0"
- cl_consoleColorGreen (green gradient) "0 - 1.0"
- cl_consoleColorBlue (blue gradient) "0 - 1.0"