Defining a new environment/command to encapsulate a colorbox

Question

I have the following working MWE file:

\documentclass{article}
\usepackage[rgb,dvipsnames,svgnames,table]{xcolor}
\usepackage{array}
\usepackage{booktabs}
%
\begin{document}
\begin{table}[!hbt]
\renewcommand{\arraystretch}{1.5}%
\centering%
\setlength{\fboxsep}{0pt}%
\arrayrulecolor{blue}%
\colorbox{lightgray}{%
\begin{tabular}{l l}
\toprule%
Column 1 & Column 2\tabularnewline% Unchanging column headers
\midrule%
One-one & One-two\tabularnewline% Changing content line one
Two-one & Two-two\tabularnewline% Changing content line two
\bottomrule%
\end{tabular}}
\end{table}
\end{document}

I would like to extract the static portions of this setup into either a new environment or a new command so that only the changing content lines will be passed to the new environment, say mytable, as

\begin{mytable}
One-one & One-two\tabularnewline% Changing content line one
Two-one & Two-two\tabularnewline% Changing content line two
\end{mytable}

or new command, say \mytable, as

\mytable{%
One-one & One-two\tabularnewline% Changing content line one
Two-one & Two-two\tabularnewline% Changing content line two
}

The \colorbox seems to throw a spanner in the works for this effort. How might I surmount this problem, please?

EDIT

In answer to @David Carlisle's query, here is the command version of what I tried:

\documentclass{article}
\usepackage[rgb,dvipsnames,svgnames,table]{xcolor}
\usepackage{array}
\usepackage{booktabs}
%
\newcommand{\mycontents}[1]{%
\renewcommand{\arraystretch}{1.5}%
\centering%
\setlength{\fboxsep}{0pt}%
\arrayrulecolor{blue}%
\colorbox{lightgray}{%
\begin{tabular}{l l}
\toprule%
Column 1 & Column 2\tabularnewline% Column headers
\midrule%
#1 % mind no braces {} around #1; that caused the error reported below
\bottomrule%
\end{tabular}}} % table environment removed as suggested by @egreg
%
\begin{document}
\mycontents{One-one & One-two\tabularnewline%
Two-one & Two-two\tabularnewline}
\end{document}

The error was:

```! Missing } inserted.
<inserted text> 
}
l.25 Two-one & Two-two\tabularnewline}
?```

Answer 1

I wouldn't use table: when there's no caption, the table environment doesn't really make sense, because if the table floats there's no way to identify it.

Instead of \begingroup and \endgroup in the code below you can use \begin{center} and \end{center} if you want all these tables to be centered. But maybe you want to have two of them side-by-side and it would be impossible.

\documentclass{article}
\usepackage[rgb,dvipsnames,svgnames,table]{xcolor}
\usepackage{array}
\usepackage{booktabs}
\newcommand{\mytable}[1]{%
  \begingroup
  \renewcommand{\arraystretch}{1.5}%
  \setlength{\fboxsep}{0pt}%
  \arrayrulecolor{blue}%
  \colorbox{lightgray}{%
    \begin{tabular}{l l}
    \toprule
    Column 1 & Column 2 \
    \midrule
    #1
    \bottomrule
    \end{tabular}%
  }%
  \endgroup
}
\begin{document}
\mytable{
  One-one & One-two \
  Two-one & Two-two \
}
\end{document}

Note that you either must always add \\ at the end or never, if you place the trailing \\ before \bottomrule.

Can the condition be relieved? Yes, but with some further work.

\documentclass{article}
\usepackage[rgb,dvipsnames,svgnames,table]{xcolor}
\usepackage{array}
\usepackage{booktabs}
\NewDocumentCommand{\mytableheaders}{}{Column 1 & Column 2}
\ExplSyntaxOn
\NewDocumentCommand{\mytable}{m}
 {
  \group_begin:
  \renewcommand{\arraystretch}{1.5}%
  \setlength{\fboxsep}{0pt}%
  \arrayrulecolor{blue}%
  \colorbox{lightgray}
   {
    \begin{tabular}{l l}
    \toprule
    \mytableheaders \
    \midrule
    \chandra_mytable_body:n { #1 }
    \bottomrule
    \end{tabular}
  }
  \group_end:
}
\cs_new_protected:Nn \chandra_mytable_body:n
 {
  \regex_match:nnTF { (\c{\} | \c{tabularnewline})\s* \Z } { #1 }
   {% there was a trailing \
    #1
   }
   {% no trailing \
    #1 \
   }
 }
\ExplSyntaxOff
\begin{document}
\mytable{
  One-one & One-two \
  Two-one & Two-two \
}
\bigskip
\mytable{
  One-one & One-two \tabularnewline
  Two-one & Two-two \tabularnewline
}
\bigskip
\mytable{
  One-one & One-two \
  Two-one & Two-two
}
\bigskip
\mytable{
  One-one & One-two \tabularnewline
  Two-one & Two-two
}
\end{document}

The argument is checked for a trailing \\ or \tabularnewline followed by spaces (that may be inserted by the endline after \\). If it's absent, one is added.