\fcolorbox with multiple colors

Question

Is it possible to draw an \fcolorbox with multiple colors inside it?

I want to draw sort of a "legend" in my beamer plot, which in the end would look something like this:

(Created with Windows Paint and MS Word)

I am familiar with fcolorbox, but can't figure out how to paint more than one color inside it.

\documentclass[]{article}
\usepackage[dvipsnames]{xcolor}
\begin{document}
%\fcolorbox{black}{ForestGreen,Magenta,red}{\vspace{0em}\hspace{1em}} --- Multiple Channels % <<< gives error
\fcolorbox{black}{red}{\vspace{0em}\hspace{1em}} --- Driver
\end{document}

Any advise would be helpful!

Answer 1

\documentclass[]{article}
\usepackage[dvipsnames]{xcolor}
\begin{document}
%\fcolorbox{black}{ForestGreen,Magenta,red}{\vspace{0em}\hspace{1em}} --- Multiple Channels % <<< gives error
{\setlength\fboxsep{0pt}%
\fbox{%
\textcolor{red}{\rule{5pt}{20pt}}%
\textcolor{blue}{\rule{5pt}{20pt}}%
\textcolor{green}{\rule{5pt}{20pt}}%
\textcolor{yellow}{\rule{5pt}{20pt}}%
}}
\end{document}

Answer 2

By coincidence, @egreg's answer yesterday ( How to construct a macro with key=value by \pgfkeys) dovetails with this one.

Adapting that answer very slightly:

MWE

\documentclass{article}
\usepackage{xcolor}
\usepackage{xparse}
\ExplSyntaxOn
\keys_define:nn { lyl/mycolorbox }
 {
  color .tl_set:N  = \l__lyl_mycolorbox_color_tl,
  text  .tl_set:N  = \l__lyl_mycolorbox_text_tl,
  color .initial:n = red!40,
  text  .initial:n = some~text,
 }
\NewDocumentCommand{\mycolorbox}{O{}}
 {
  \group_begin:
  \keys_set:nn { lyl/mycolorbox } { #1 }
  \colorbox{\l__lyl_mycolorbox_color_tl}{\l__lyl_mycolorbox_text_tl}
  \group_end:
 }
\ExplSyntaxOff
\begin{document}
\mycolorbox[color=blue!20]
\mycolorbox[text=This is a practice. Default colour.]
\mycolorbox[color=blue!20, text=This is a practice.]
\mycolorbox[text=\strut] 
: with strut
\mycolorbox[text=\strut\ ] 
: strut with space
\mycolorbox[text=\strut\ ,color=red]
\mycolorbox[text=\strut\ ,color=blue]
\mycolorbox[text=\strut\ ,color=green]
\mycolorbox[text=\strut\ ,color=yellow]
 : set of boxes
\setlength{\fboxsep}{5pt}
\mycolorbox[text=\strut\ ,color=red]
\mycolorbox[text=\strut\ ,color=blue]
\mycolorbox[text=\strut\ ,color=green]
\mycolorbox[text=\strut\ ,color=yellow] 
: fboxsep=5pt
\mycolorbox[text=\strut R ,color=red]%
\mycolorbox[text=\strut\textcolor{white}{B} ,color=blue]%
\mycolorbox[text=\strut G ,color=green]%
\mycolorbox[text=\strut Y ,color=yellow] 
: no spaces
\fbox{%
\mycolorbox[text=\strut R ,color=red]%
\mycolorbox[text=\strut\textcolor{white}{B} ,color=blue]%
\mycolorbox[text=\strut G ,color=green]%
\mycolorbox[text=\strut Y ,color=yellow]%
} 
: inside fbox
\fcolorbox{violet}{blue!20}{%
\mycolorbox[text=\strut R ,color=red]%
\mycolorbox[text=\strut\textcolor{white}{B} ,color=blue]%
\mycolorbox[text=\strut G ,color=green]%
\mycolorbox[text=\strut Y ,color=yellow]%
} 
: inside fcolorbox
\setlength{\fboxrule}{2pt}
\fcolorbox{violet}{blue!20}{%
\mycolorbox[text=\strut R ,color=red]%
\mycolorbox[text=\strut\textcolor{white}{B} ,color=blue]%
\mycolorbox[text=\strut G ,color=green]%
\mycolorbox[text=\strut Y ,color=yellow]%
} 
: fboxrule = 2pt
\fcolorbox{violet}{blue!20}{%
\mycolorbox[text=\strut\sffamily red ,color=red]%
\mycolorbox[text=\strut\sffamily\textcolor{white}{blue} ,color=blue]%
\mycolorbox[text=\strut\sffamily green ,color=green]%
\mycolorbox[text=\strut\sffamily yellow ,color=yellow]%
}
\end{document}

Answer 3

Pursuing David's idea, but letting TeX do the calculations…

\documentclass{article}
\usepackage[dvipsnames]{xcolor}
\ExplSyntaxOn
\NewDocumentCommand{\colorlegend}{O{2em}m}
 {% #1 = total width, #2 = list of color names
  \group_begin:
  \setlength{\fboxsep}{0pt}
  \fbox { \tush_colorlegend:nn { #1 } { #2 } }
  \group_end:
 }
\seq_new:N \l__tush_colorlegend_colors_seq
\dim_new:N \l__tush_colorlegend_wd_dim
\cs_new_protected:Nn \tush_colorlegend:nn
 {
  \seq_set_from_clist:Nn \l__tush_colorlegend_colors_seq { #2 }
  \dim_set:Nn \l__tush_colorlegend_wd_dim { #1 / \seq_count:N \l__tush_colorlegend_colors_seq }
  \seq_map_inline:Nn \l__tush_colorlegend_colors_seq
   {
    \textcolor{##1}{\rule{\l__tush_colorlegend_wd_dim}{0.8\ht\strutbox}}
   }
 }
\ExplSyntaxOff
\begin{document}
\colorlegend{ForestGreen,Apricot,Magenta,TealBlue,YellowOrange,green!20} -- Multiple channels
\colorlegend{red} -- Driver
\colorlegend[40pt]{ForestGreen,Apricot,Magenta,TealBlue,YellowOrange,green!20} -- Multiple channels
\colorlegend[30pt]{red} -- Driver
\end{document}