\documentclass[a4paper,12pt]{article}
\usepackage{amsmath,amsthm,amssymb}
\usepackage{color}
\usepackage{xepersian}
\settextfont{XB Zar}
\setdigitfont{XB Zar}
\renewcommand\labelenumi{\textcolor{blue}{\theenumi}.}
\makeatletter
\newenvironment{solution}[1][\solutionname]{\par
  \pushQED{\qed}%
  \normalfont \topsep6\p@\@plus6\p@\relax
  \trivlist
  \item[\hskip\labelsep
        \itshape
    #1\@addpunct{.}]\ignorespaces
}{%
  \popQED\endtrivlist\@endpefalse
}
\providecommand{\solutionname}{\textcolor{blue}{حل}}
\makeatother
\begin{document}
\begin{enumerate}
\item
\item
\item
\end{enumerate}
\begin{solution}
این یک راه‌حل است.
\end{solution}
\end{document}