[Tex/LaTex] color an item in an enumerated list

#enumeratecolorenumitem

I have an enumerated list, for which I'm using enumitem because I want to resume the enumeration, and one item is rendered in a faded color using xcolor

\usepakage{enumitem, xcolor}
% ...
\begin{enumerate}
\item First.
\end{enumerate}
other stuff
\begin{enumerate}[resume]
\item Second.
\item \textcolor{gray}{Third.}
\item Fourth.
\end{enumerate}

I'd like to have the label of "Third." rendered in the same faded color, and because I've seen Bolding a single number in a enumerated list I defined

newcommand{\fadeditem}{\item[\stepcounter{enumi}\textcolor{gray}{\arabic{enumi}.}]}

and it works (it's not general, but it works) but now it's not enough… I realize that what I want is a command that takes care also
of the item text

What I have now

\fadeditem \textcolor{gray}{Bla bla bla.}

What I would like

\itemcolor{gray} Bla bla bla.

Addendum #1

David Carlisle, in a comment, suggested 

\newcommand\itemcolor[1]{\fadeditem{#1}\textcolor{#1}}

and this deals with my task of today, writing optional questions in a list of questions.

An open part of the question is then a generalization of the problem,
defining an \itemcolor{somecolor} command that just works in any (in most?) lists…

Best Answer

EDITED to limit the scope of the renewed \item to the newly defined cenumerate environment.

\documentclass{article}
\usepackage{enumitem, xcolor}
\let\svitem\item
\newenvironment{cenumerate}[1][\relax]{\renewcommand\item[1][black]{\color{##1}\svitem}
  \ifx\relax#1\enumerate\else\enumerate[#1]\fi}{\endenumerate}
\begin{document}
\begin{cenumerate}
\item First.
\end{cenumerate}
other stuff
\begin{cenumerate}[resume]
\item Second.
\item[gray] Third.
\item Fourth.
\item[red][*] Star item.
\end{cenumerate}
\begin{description}
\item[Rayleigh Quotient] Choose an appropriate shape function
\end{description}
\end{document}

enter image description here

More simply without redefining \item, but with a little extra typing, just invoke \color in a group, as needed, to get the same result:

\documentclass{article}
\usepackage{enumitem, xcolor}

\begin{document}
\begin{enumerate}
\item First.
\end{enumerate}
other stuff
\begin{enumerate}[resume]
\item Second.
{\color{gray}\item Third.}
\item Fourth.
{\color{red}\item[*] Star item.}
\end{enumerate}
\end{document}
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