REDBG -- start red colored background section

• REDBG is one of the rendering shortcut settings predefined in TWikiPreferences. See the section rendering shortcut settings in that topic for a complete list of background colors.
• Syntax: %REDBG% red background %ENDBG%
• Expands to:
  red background
• Note: %REDBG% area must end with %ENDBG%.
• Category: FormattingAndRenderingVariables
• Related: ENDBG, RED, TWikiPreferences rendering shortcuts, StandardColors