Mono C＃奇怪的控制台颜色

Question

I have this Console art function,

public static void Ask(string message)
{
    ConsoleColor previousColor = Console.ForegroundColor;
    Console.ForegroundColor = ConsoleColor.White;
    Console.Write (message);
    Console.Write (" : ");
    Console.ForegroundColor = previousColor;
}

This is my Main()

Console.WriteLine("Hello World");
Ask("Roll No");

The two white colors printed aren't the same, as shown below

In the debugger, I can see that previousColor is also ConsoleColor.White .

Answer 1

This is an area which occasionally causes confusion. Call it a limitation rather than a bug.

There are two factors which are relevant:

1. most terminals which implement color in X do this as xterm and rxvt have done since the mid-1990s: the terminal originally could have the default foreground and background colors specified, and ANSI (and extended) colors were added later. Unlike the Linux console, there is no guarantee that the default and ANSI colors are related.

   VTE (which is the functional part of Terminal) followed that design, as did Konsole.

   Quoting from xterm's manual description of reverseVideo shows that there is a distinction between ANSI colors and the default colors used for the terminal:

Other control sequences can alter the foreground and background
               colors which are used:

               o   Programs can also use the ANSI color control  sequences  to
                   set the foreground and background colors.

               o   Extensions  to the ANSI color controls (such as 16-, 88- or
                   256-colors) are treated similarly to the ANSI control.

               o   Using other control sequences (the  "dynamic  colors"  fea-
                   ture),  a  program can change the foreground and background
                   colors.

2. Mono Console is written to imitate (and in some parts, adapt chunks of) ncurses. The ncurses FAQ Ncurses resets my colors to white/black notes that ncurses assumes the default colors are white on black — Console follows that design as well.

   It could have followed ncurses a bit further to be more aware of the distinction between an explicit "white" done by telling the terminal to draw white text versus an implicit "white" (by resetting the colors to their default values).