Change color for each item in itemize

Question

Consider the following simple code:

\documentclass[11pt]{article} 
\begin{document}        
\begin{itemize}
    \item plain text
    \item I want this to be blue
    \item another text
\end{itemize}
\end{document}

The result of the code is

Now, suppose that I want to make the text color of the second item blue. One can manually use the textcolor command, but the thing is that in my real example there are many places to change the text, and such places are frequently modified. Hence, it is desirable to write a macro to change the color simply.

Question: How can I define custom command like \blueitem, such that replacing \item to \blueitem in the above code gives the desired result? Or, as an alternative, one can also think of a macro that using \item[color=blue] instead of \item gives the result.

Edit: The answer by Sandy G does not work when used with the proof environment. For example:

\documentclass[11pt]{article}
\usepackage{amsthm}
\usepackage{xcolor}
\let\olditem\item\renewcommand{\item}[1][black]{\color{#1}\olditem} 
\begin{document}
\begin{itemize}
    \item[blue] abc
    \begin{proof}
        abc.
    \end{proof}
\end{itemize}
\end{document}

This code gives an error message

Package xcolor Error: Undefined color `\hskip \labelsep \itshape Proof\relax '. a

and the result is:

Note that there is no "Proof." symbol.

Answer 1

You can redefine \item to accept an optional argument for the color using xcolor.

\documentclass[11pt]{article} 
\usepackage{xcolor}

\let\olditem\item\renewcommand{\item}[1][black]{\color{#1}\olditem}

\begin{document}        
\begin{itemize}
    \item plain text
    \item[blue] I want this to be blue
    \item[red] another text
    \item one more
\end{itemize}
\end{document}

The main problem with this approach is that some environments use lists, and there are undesired consequences. Notably, a proof from amsthm is a list, so this won't work. A better solution is to make a new command, for example \citem that accepts an optional color argument:

\newcommand{\citem}[1][black]{\color{#1}\item}

One downside to this approach is that \citem will change the color of all \items below it in the list. So use \citem with no color (black is the default) to change back to black for the rest of the list. Then you can use \item and \citem in the same list.

\documentclass[11pt]{article}
\usepackage{amsthm}
\usepackage{xcolor}
\newcommand{\citem}[1][black]{\color{#1}\item} 
\begin{document}

\begin{itemize}
  \citem[blue] abc
    \begin{proof}
        abc.
    \end{proof}
  \citem[red] abc
    \begin{proof}
        abc.
    \end{proof}
    
\end{itemize}
\end{document}

Answer 2

This is one way to do it:

\documentclass[11pt]{article}                                                     
\usepackage{xcolor}                                                               
                                                                                  
\newcommand\colitem[2]{%                                                          
  {\color{#1}\item {#2}}                                                          
}                                                                                 
                                                                                  
\newcommand\reditem[1]{%                                                          
  \colitem{red}{#1}                                                               
}                                                                                 
                                                                                  
\newcommand\blueitem[1]{%                                                         
  \colitem{blue}{#1}                                                              
}                                                                                 
                                                                                  
\begin{document}                                                                  
\begin{itemize}                                                                   
    \reditem {plain text}                                                         
    \blueitem {I want this to be blue}                                            
    \item another text                                                            
\end{itemize}                                                                     
\end{document}

The output will be like this: