How do I change the full background color of the console window in C#?

You need to clear the console window AFTER setting the colors but BEFORE you write the text...

Console.ForegroundColor = ConsoleColor.Red;
Console.BackgroundColor = ConsoleColor.Green;

Console.Clear();

Console.WriteLine("Hello World");

Console.ReadLine();

Pardon the shameless self-promotion, but I've created a small plugin (available on NuGet) that allows you to add any (if supported by your terminal) color to your console output, without the limitations of the classic solutions.

It works by extending the String object, and the syntax is very simple:

"colorize me".Pastel("#1E90FF");