I'm assuming you mean the 'Colorized Example Code' widget, used with the 'Language Filtered Section' option?
If so, you can define a style rule in your project to control the background. The style rule needs to match the .LanguageFiltered class. Here's an example:
DIV.LanguageSpecific
{
background: #e0e0e0
}
Let me know if you need any more information, or if it is a different widget type you are using.