You can control the characteristics of your xterm when you invoke it. For example, you can use the -bg option to change the background color and the -e option (must be last) to specify the command to be run in the xterm. So, to run bash on a magenta background, you would invoke xterm as: xterm -bg magenta -e bash
Check the properties of whatever icon/launcher you are using to start xterm and modify the xterm command line to include the options you want. Alternatively, you can enter the xterm command with your desired options in a command window.
Hope this helps.