This happens because your language definition is too "poor" at the moment; you haven't declared strings, keywords, comments... Depending on the specificity of your language, there are several options: you could use the starred version of literate, so the replacements you declared won't be made on strings and comments, and define some appropriate strings. In the following example, everything between _ and ( and between _ and = will be treated as a string:
\documentclass[fleqn, a4paper]{article}
\usepackage{listings}
\usepackage{color}
\lstdefinelanguage{mylang}{%
basicstyle=\ttfamily,%
literate=*{0}{{\textcolor{blue}{0}}}{1}%
{1}{{\textcolor{blue}{1}}}{1}%
{2}{{\textcolor{blue}{2}}}{1}%
{3}{{\textcolor{blue}{3}}}{1}%
{4}{{\textcolor{blue}{4}}}{1}%
{5}{{\textcolor{blue}{5}}}{1}%
{6}{{\textcolor{blue}{6}}}{1}%
{7}{{\textcolor{blue}{7}}}{1}%
{8}{{\textcolor{blue}{8}}}{1}%
{9}{{\textcolor{blue}{9}}}{1}%
{.0}{{\textcolor{blue}{.0}}}{1}% Following is to ensure that only periods
{.1}{{\textcolor{blue}{.1}}}{1}% followed by a digit are changed.
{.2}{{\textcolor{blue}{.2}}}{1}%
{.3}{{\textcolor{blue}{.3}}}{1}%
{.4}{{\textcolor{blue}{.4}}}{1}%
{.5}{{\textcolor{blue}{.5}}}{1}%
{.6}{{\textcolor{blue}{.6}}}{1}%
{.7}{{\textcolor{blue}{.7}}}{1}%
{.8}{{\textcolor{blue}{.8}}}{1}%
{.9}{{\textcolor{blue}{.9}}}{1}%
{\ }{{ }}{1}% handle the space
,%
string=[s]{_}{=},
string=[s]{_}{(},
stringstyle=\ttfamily,
showstringspaces=false
}
\begin{document}
\begin{lstlisting}[language=mylang]
{
_SetCalibTableName("lorem",100);
g_Met_strReferenceName1=Met_strReferenceName;
}
\end{lstlisting}
\end{document}
But this could not be the best approach, depending on the language you are trying to define (perhaps this approach would involve considering so many cases that it's not viable, or some objects that shouldn't be treated as strings will be considered erroneously as such).
Another option would be to escape those numbers for which you don't want the replacement to be done; for example, assuming that ! won't be used with any specific meaning in your language, you could say:
\documentclass[fleqn, a4paper]{article}
\usepackage{listings}
\usepackage{color}
\lstdefinelanguage{mylang}{%
basicstyle=\ttfamily,%
literate=*{0}{{\textcolor{blue}{0}}}{1}%
{1}{{\textcolor{blue}{1}}}{1}%
{2}{{\textcolor{blue}{2}}}{1}%
{3}{{\textcolor{blue}{3}}}{1}%
{4}{{\textcolor{blue}{4}}}{1}%
{5}{{\textcolor{blue}{5}}}{1}%
{6}{{\textcolor{blue}{6}}}{1}%
{7}{{\textcolor{blue}{7}}}{1}%
{8}{{\textcolor{blue}{8}}}{1}%
{9}{{\textcolor{blue}{9}}}{1}%
{.0}{{\textcolor{blue}{.0}}}{1}% Following is to ensure that only periods
{.1}{{\textcolor{blue}{.1}}}{1}% followed by a digit are changed.
{.2}{{\textcolor{blue}{.2}}}{1}%
{.3}{{\textcolor{blue}{.3}}}{1}%
{.4}{{\textcolor{blue}{.4}}}{1}%
{.5}{{\textcolor{blue}{.5}}}{1}%
{.6}{{\textcolor{blue}{.6}}}{1}%
{.7}{{\textcolor{blue}{.7}}}{1}%
{.8}{{\textcolor{blue}{.8}}}{1}%
{.9}{{\textcolor{blue}{.9}}}{1}%
{\ }{{ }}{1}% handle the space
,%
escapeinside={!!}
}
\begin{document}
\begin{lstlisting}[language=mylang]
{
_SetCalibTableName("lorem",100);
g_Met_strReferenceName!1!=Met_strReferenceName;
}
\end{lstlisting}
\end{document}
Another option (similar in spirit to the last one) would be to set mathescape=true and surround the numbers in the variable names with $...$:
\documentclass[fleqn, a4paper]{article}
\usepackage{listings}
\usepackage{color}
\lstdefinelanguage{mylang}{%
basicstyle=\ttfamily,%
literate=*{0}{{\textcolor{blue}{0}}}{1}%
{1}{{\textcolor{blue}{1}}}{1}%
{2}{{\textcolor{blue}{2}}}{1}%
{3}{{\textcolor{blue}{3}}}{1}%
{4}{{\textcolor{blue}{4}}}{1}%
{5}{{\textcolor{blue}{5}}}{1}%
{6}{{\textcolor{blue}{6}}}{1}%
{7}{{\textcolor{blue}{7}}}{1}%
{8}{{\textcolor{blue}{8}}}{1}%
{9}{{\textcolor{blue}{9}}}{1}%
{.0}{{\textcolor{blue}{.0}}}{1}% Following is to ensure that only periods
{.1}{{\textcolor{blue}{.1}}}{1}% followed by a digit are changed.
{.2}{{\textcolor{blue}{.2}}}{1}%
{.3}{{\textcolor{blue}{.3}}}{1}%
{.4}{{\textcolor{blue}{.4}}}{1}%
{.5}{{\textcolor{blue}{.5}}}{1}%
{.6}{{\textcolor{blue}{.6}}}{1}%
{.7}{{\textcolor{blue}{.7}}}{1}%
{.8}{{\textcolor{blue}{.8}}}{1}%
{.9}{{\textcolor{blue}{.9}}}{1}%
{\ }{{ }}{1}% handle the space
,%
mathescape=true
}
\begin{document}
\begin{lstlisting}[language=mylang]
{
_SetCalibTableName("lorem",100);
g_Met_strReferenceName$1$=Met_strReferenceName;
}
\end{lstlisting}
\end{document}
