listing background color not exactly the same

Question

I like SO code section colors. so I wish to use it as code listings box background color.

I use a screen capture tool to capture the code background color to png, then use GIMP tool to check the RGB value is (245,245,245). but when I use below code to define such color and use it as background color, it seems the color too dark then SO code colors.

\documentclass[border=2pt]{standalone}
%\usepackage[a4paper,margin=1cm]{geometry}

\usepackage{listings}
\usepackage{xcolor}

\definecolor{mygray}{RGB}{245,245,245}
\definecolor{mygreen}{rgb}{0,0.6,0}
\definecolor{mygray}{rgb}{0.5,0.5,0.5}
\definecolor{mymauve}{rgb}{0.58,0,0.82}

\lstset{ %
  backgroundcolor=\color{mygray},   % choose the background color; you must add \usepackage{color} or \usepackage{xcolor}
  basicstyle=\footnotesize,        % the size of the fonts that are used for the code
  breakatwhitespace=false,         % sets if automatic breaks should only happen at whitespace
  breaklines=true,                 % sets automatic line breaking
  captionpos=b,                    % sets the caption-position to bottom
  commentstyle=\color{mygreen},    % comment style
  deletekeywords={...},            % if you want to delete keywords from the given language
  escapeinside={\%*}{*)},          % if you want to add LaTeX within your code
  extendedchars=true,              % lets you use non-ASCII characters; for 8-bits encodings only, does not work with UTF-8
  frame=single,                    % adds a frame around the code
  keepspaces=true,                 % keeps spaces in text, useful for keeping indentation of code (possibly needs columns=flexible)
  keywordstyle=\color{blue},       % keyword style
  language=c,                 % the language of the code
  otherkeywords={*,...},           % if you want to add more keywords to the set
  numbers=left,                    % where to put the line-numbers; possible values are (none, left, right)
  numbersep=5pt,                   % how far the line-numbers are from the code
  numberstyle=\tiny\color{mygray}, % the style that is used for the line-numbers
  rulecolor=\color{black},         % if not set, the frame-color may be changed on line-breaks within not-black text (e.g. comments (green here))
  showspaces=false,                % show spaces everywhere adding particular underscores; it overrides 'showstringspaces'
  showstringspaces=false,          % underline spaces within strings only
  showtabs=false,                  % show tabs within strings adding particular underscores
  stepnumber=2,                    % the step between two line-numbers. If it's 1, each line will be numbered
  stringstyle=\color{mymauve},     % string literal style
  tabsize=2,                       % sets default tabsize to 2 spaces
  title=\lstname                   % show the filename of files included with \lstinputlisting; also try caption instead of title
}

\begin{document}
\begin{lstlisting}
#include <stdio.h>

int main() {
    print "hello world\n";
}
\end{lstlisting}
\end{document}

Output

What's wrong with my background color code?

Answer 1

Package xcolor has two variants to set up RGB colorspace, depending on whether capital letters are used or nor (RGB vs. rgb):

\definecolor{mygray}{RGB}{245,245,245}

which is well-known representation where min is 0 and max is 255, and

\definecolor{mygray}{rgb}{0.5,0.5,0.5}

which has another scale where min is 0.0 and max is 1.0.

In your MWE you at third \definecolor you in fact redefined mygray to the darker variant, since the following lines are equal:

\definecolor{mygray}{rgb}{0.5,0.5,0.5}
\definecolor{mygray}{RGB}{127,127,127}

If you remove this line, everything looks nice:

\documentclass[border=2pt]{standalone}
%\usepackage[a4paper,margin=1cm]{geometry}

\usepackage{listings}
\usepackage{xcolor}

\definecolor{mygray}{RGB}{245,245,245}
\definecolor{mygreen}{rgb}{0,0.6,0}
%\definecolor{mygray}{rgb}{0.5,0.5,0.5}
\definecolor{mymauve}{rgb}{0.58,0,0.82}

\lstset{ %
    backgroundcolor=\color{mygray},   % choose the background color; you must add \usepackage{color} or \usepackage{xcolor}
    basicstyle=\footnotesize,        % the size of the fonts that are used for the code
    breakatwhitespace=false,         % sets if automatic breaks should only happen at whitespace
    breaklines=true,                 % sets automatic line breaking
    captionpos=b,                    % sets the caption-position to bottom
    commentstyle=\color{mygreen},    % comment style
    deletekeywords={...},            % if you want to delete keywords from the given language
    escapeinside={\%*}{*)},          % if you want to add LaTeX within your code
    extendedchars=true,              % lets you use non-ASCII characters; for 8-bits encodings only, does not work with UTF-8
    frame=single,                    % adds a frame around the code
    keepspaces=true,                 % keeps spaces in text, useful for keeping indentation of code (possibly needs columns=flexible)
    keywordstyle=\color{blue},       % keyword style
    language=c,                 % the language of the code
    otherkeywords={*,...},           % if you want to add more keywords to the set
    numbers=left,                    % where to put the line-numbers; possible values are (none, left, right)
    numbersep=5pt,                   % how far the line-numbers are from the code
    numberstyle=\tiny\color{mygray}, % the style that is used for the line-numbers
    rulecolor=\color{black},         % if not set, the frame-color may be changed on line-breaks within not-black text (e.g. comments (green here))
    showspaces=false,                % show spaces everywhere adding particular underscores; it overrides 'showstringspaces'
    showstringspaces=false,          % underline spaces within strings only
    showtabs=false,                  % show tabs within strings adding particular underscores
    stepnumber=2,                    % the step between two line-numbers. If it's 1, each line will be numbered
    stringstyle=\color{mymauve},     % string literal style
    tabsize=2,                       % sets default tabsize to 2 spaces
    title=\lstname                   % show the filename of files included with \lstinputlisting; also try caption instead of title
}

\begin{document}
    \begin{lstlisting}
    #include <stdio.h>

    int main() {
    print "hello world\n";
    }
    \end{lstlisting}
\end{document}

Also notice that mygreen and mymauve are also very dark, since they are also identical to

\definecolor{mygreen}{RGB}{0,153,0}
\definecolor{mymauve}{RGB}{148,0,209}

but in another scale.