Fontcolor in listing

I want to write a listing for python code. My problem, the zero by x = SUM('ZM_test'[testcol 0AN]) is in black fontcolor and not in green. My style settings for the listing looks like this:

\documentclass[12pt,a4paper]{report}
\usepackage[utf8]{inputenc}
\usepackage[german]{babel}
\usepackage[left=4cm,right=3cm,top=2.5cm,bottom=2.5cm]{geometry}

\usepackage{listings}
\usepackage{color}
\definecolor{keywords}{RGB}{255,0,90}
\definecolor{comments}{RGB}{0,0,113}
\definecolor{red}{RGB}{160,0,0}
\definecolor{green}{RGB}{0,150,0}
\lstset{language=Python, 
    basicstyle=\ttfamily\footnotesize, 
    keywordstyle=\color{keywords},
    commentstyle=\color{comments},
    stringstyle=\color{red},
    showstringspaces=false,
    identifierstyle=\color{green},
    %procnamekeys={def,class}
    numbers=left,
    xleftmargin=2em,
    frame=single,
    framexleftmargin=1.5em
}

\begin{document}
\begin{lstlisting}[language=Python, caption=xy, label=xy, numbers =left, frame= lines, gobble = 0]
x = SUM('ZM_test'[testcol 0AN])
y = SUM('ZM_test'[testcol bAN])
\end{lstlisting}
\end{document}

Do you know, why the zero has the fontcolor "black" and not "green"? I want the zero green like the "b" in y = SUM('ZM_test'[testcol bAN])

EDIT: That is not python code, but it should be the python style. Best regards Christian

Solution

You could try the approach from https://tex.stackexchange.com/a/42895

\documentclass[12pt,a4paper]{report}
\usepackage[utf8]{inputenc}
\usepackage[german]{babel}
\usepackage[left=4cm,right=3cm,top=2.5cm,bottom=2.5cm]{geometry}

\usepackage{listings}
\usepackage{xcolor}
\definecolor{keywords}{RGB}{255,0,90}
\definecolor{comments}{RGB}{0,0,113}
\definecolor{red}{RGB}{160,0,0}
\definecolor{green}{RGB}{0,150,0}
\lstset{language=Python, 
    basicstyle=\ttfamily\footnotesize, 
    keywordstyle=\color{keywords},
    commentstyle=\color{comments},
    stringstyle=\color{red},
    showstringspaces=false,
    identifierstyle=\color{green},
    %procnamekeys={def,class}
    numbers=left,
    xleftmargin=2em,
    frame=single,
    framexleftmargin=1.5em
}


\lstset{literate=%
   *{0}{{{\color{green}0}}}1
    {1}{{{\color{green}1}}}1
    {2}{{{\color{green}2}}}1
    {3}{{{\color{green}3}}}1
    {4}{{{\color{green}4}}}1
    {5}{{{\color{green}5}}}1
    {6}{{{\color{green}6}}}1
    {7}{{{\color{green}7}}}1
    {8}{{{\color{green}8}}}1
    {9}{{{\color{green}9}}}1
}

\begin{document}
\begin{lstlisting}[language=Python, caption=xy, label=xy, numbers =left, frame= lines, gobble = 0]
x = SUM('ZM_test'[testcol 0AN])
y = SUM('ZM_test'[testcol bAN])
\end{lstlisting}
\end{document}