documentclass{article}
usepackage{xcolor}
usepackage{listings}
lstset{
    keywordstyle=color{blue},
    identifierstyle=color{red},
}
lstnewenvironment{algol}{lstset{language=algol}}{}
begin{document}

begin{lstlisting}
foo
end{lstlisting}

begin{algol}
int foo
end{algol}

end{document}

documentclass{article}
usepackage{xcolor}
usepackage{listings}
lstset{
    identifierstyle=color{red},
}
begin{document}
begin{lstlisting}
foo
end{lstlisting}
end{document}