SetConsoleBackground(ch)
ch. The character must be passed as a numeric value, not a string. For
normal characters ch simply specifies the Unicode codepoint of the respective character,
e.g. 65 for 'A'. The ch argument, however, can also be a special character code composed by
the MakeConsoleChr() function. This function allows you to merge text formatting
styles into the character code and it also supports special character codes like arrows
or border bits. See MakeConsoleChr for details.
You must enable advanced console mode using EnableAdvancedConsole() before you can use this function. See EnableAdvancedConsole for details.
EnableAdvancedConsole()
SetConsoleBackground('=')
RefreshConsole()
The code above fills the console background with '=' characters.