Background color for all existing floats

Question

I'm using this code to add background color to all floating elements:

\makeatletter
\def\foo#1\normalcolor\vbox\bgroup#2!!{%
\def@xfloat ##1[##2]{#1%
 \normalcolor
      \hbox\bgroup{\color{yellow}\leaders\vrule\hskip\columnwidth\hskip-\columnwidth}%
      \vbox \bgroup\aftergroup\egroup
#2}}
\expandafter\foo@xfloat{#1}[#2]!!
\makeatother

but only part of the table that occupies two columns in a two-column document will change color. I want to know how to add a background color based on the actual width of the table/picture?

\documentclass[11pt,a4paper,twocolumn,english]{article}
\usepackage{lipsum}
\usepackage{xcolor}
\makeatletter
\def\foo#1\normalcolor\vbox\bgroup#2!!{%
\def@xfloat ##1[##2]{#1%
 \normalcolor
      \hbox\bgroup{\color{yellow}\leaders\vrule\hskip\columnwidth\hskip-\columnwidth}%
      \vbox \bgroup\aftergroup\egroup
#2}}
\expandafter\foo@xfloat{#1}[#2]!!
\makeatother
\title{Two column test}
\begin{document}
\maketitle
\lipsum
 \begin{table}[h]
 \small
 \centering
 \caption{Simuleringsresultat av beräkning av $\pi$ genom Monte Carlo.}
 \begin{tabular}{|p{2.1cm}|p{2.1cm}|p{2.1cm}|p{2.1cm}|p{2.1cm}|p{2.1cm}|p{2.1cm}| }
   \hline
   \multicolumn{7}{|c|}{En beräkning av $\pi$ genom Monte Carlo} \
    \hline
Antal \linebreak partiklar & Värde 1 & Värde 2 & Värde 3 & Värde 4 &   Värde 5 & Medelvärde\
 \hline
 $10^0$  & 4    & 4 &   4  & 4 & 0 & 3,2      \
 $10^1$ & 3,2  & 2,4   & 4,0  & 3,6  & 3,6 & 3,36  \
 $10^2$ & 3,56 & 2,92 &  3,32   &  3,04  & 3,36 & 3,24    \
 $10^3$ & 3,208 & 3,160 &  3,108  & 3,136  & 3,136 & 3,1496  \
 $10^4$ & 3,1404  & 3,1288 & 3,1460  & 3,1572 & 3,1308 & 3,14064  \
 $10^5$ & 3,13468  & 3,14724   & 3,14316 & 3,14124  & 3,14248 & 3,14176     \
 $10^6$ & 3,14286  & 3,146348 & 3,142648  &  3,141184  & 3,142144 & 3,1430368 \
 $10^7$ & 3,1421208  & 3,141374 & 3,1414892  & 3,1413988  & 3,1416936 & 3,14161528 \
 $10^8$ & 3,14138248  & 3,14127896 & 3,14172908  & 3,14154640 & 3,14178604 & 3,141544592 \
 $10^9$ & 3,1416602762  & 3,1415840040 & 3,1415684520   &  3,1415948080 & 3,1416119840 & 3.1416039048   \
\hline
\multicolumn{7}{|c|}{$\pi = 3.1415926535 $ }  \
\hline
\end{tabular}
\end{table}
\end{document}

Answer 1

Replacing two occurrences of \columnwidth with \textwidth in the redefinition of \@xfloat when it is called by a starred float environment, does the work. BTW your table is too wide.

Package showframe is loaded just to show page frame(s).

\documentclass[11pt,a4paper,twocolumn,english]{article}
\usepackage{lipsum}
\usepackage{xcolor}
\usepackage{showframe}
\makeatletter
\newif\iffloat@twocolumn
% redefine @dblfloat
\def@dblfloat{%
  \if@twocolumn
    \let\reserved@a@dbflt
    \float@twocolumntrue
  \else
    \let\reserved@a@float
  \fi
  \reserved@a}
% based on https://tex.stackexchange.com/a/106906
% added \iffloat@twocolumn ... \else ... \fi
\def\foo#1\normalcolor\vbox\bgroup#2!!{%
\def@xfloat ##1[##2]{#1%
 \normalcolor
      \hbox\bgroup{%
        \color{yellow}%
        \iffloat@twocolumn
          \leaders\vrule\hskip\textwidth\hskip-\textwidth
        \else
          \leaders\vrule\hskip\columnwidth\hskip-\columnwidth
        \fi}%
      \vbox \bgroup\aftergroup\egroup
#2}}
\expandafter\foo@xfloat{#1}[#2]!!
\makeatother
\title{Two column test}
\begin{document}
\maketitle
\lipsum[1]
\begin{table}[h]
  \centering
  content
\end{table}
\lipsum
 \begin{table}[h]
 \small
 \centering
 \caption{Simuleringsresultat av beräkning av $\pi$ genom Monte Carlo.}
 \begin{tabular}{|p{2.1cm}|p{2.1cm}|p{2.1cm}|p{2.1cm}|p{2.1cm}|p{2.1cm}|p{2.1cm}| }
   \hline
   \multicolumn{7}{|c|}{En beräkning av $\pi$ genom Monte Carlo} \
    \hline
Antal \linebreak partiklar & Värde 1 & Värde 2 & Värde 3 & Värde 4 &   Värde 5 & Medelvärde\
 \hline
 $10^0$  & 4    & 4 &   4  & 4 & 0 & 3,2      \
 $10^1$ & 3,2  & 2,4   & 4,0  & 3,6  & 3,6 & 3,36  \
 $10^2$ & 3,56 & 2,92 &  3,32   &  3,04  & 3,36 & 3,24    \
 $10^3$ & 3,208 & 3,160 &  3,108  & 3,136  & 3,136 & 3,1496  \
 $10^4$ & 3,1404  & 3,1288 & 3,1460  & 3,1572 & 3,1308 & 3,14064  \
 $10^5$ & 3,13468  & 3,14724   & 3,14316 & 3,14124  & 3,14248 & 3,14176     \
 $10^6$ & 3,14286  & 3,146348 & 3,142648  &  3,141184  & 3,142144 & 3,1430368 \
 $10^7$ & 3,1421208  & 3,141374 & 3,1414892  & 3,1413988  & 3,1416936 & 3,14161528 \
 $10^8$ & 3,14138248  & 3,14127896 & 3,14172908  & 3,14154640 & 3,14178604 & 3,141544592 \
 $10^9$ & 3,1416602762  & 3,1415840040 & 3,1415684520   &  3,1415948080 & 3,1416119840 & 3.1416039048   \
\hline
\multicolumn{7}{|c|}{$\pi = 3.1415926535 $ }  \
\hline
\end{tabular}
\end{table}
\end{document}