Latex: use color without defining a new color

Question

Is it possible to use a new color without defining a new color like \definecolor{mycolor}{HTML}{a65dbd}? It is indeed cumbersome to use when the color is used only once, and can easily lead to conflicts if multiple parts of the file use the same color name for different colors (in particular, no error is given if we use \definecolor{mycolor} twice, so the colors only appears to be wrong for no apparent reason).

As HTML colors are easy to copy/paste between programs, I'd love to be able to do something like:

\textcolor{HTML(00AA00)}{\textbf{This is not working}}

MWE:

\documentclass{article}
\usepackage{xcolor}
\usepackage{tikz}
\usepackage{verbatim}
\definecolor{mycolor}{HTML}{a65dbd} % Equal to RGB(166,93,189).
\begin{document}
\noindent
\textcolor{mycolor}{\textbf{This is my color but annoying to use.}}\\
\textcolor{red!65!green!36!blue!74!}{\textbf{This is better but not accurate nor easily copy/pastable.}}\\
\textcolor[HTML]{a65dbd}{\textbf{This is working, but not generalizable (tikz, tabularray\dots).}}\\
\verb|\tikz \node[text=[HTML]{a65dbd]{This is not working};|
\end{document}

EDIT

Phelype proposed in comments to use \textcolor[HTML]{00AA00}{...}, unfortunately it does not generalize to other commands. For instance, this is not working in tikz, nor in tabularray cell colors:

\tikz \node[text=[HTML]{a65dbd]{This is not working};

Wouldn't it be possible to define a generic color taking arguments (like green!50!white which works for both tikz, tabularray, textcolor...) but taking as input an HTML color description?

EDIT

I created a feature request here https://github.com/latex3/xcolor/issues/13 but if someone has a solution is the meantime, I'd be interested to hear it.

Answer 1

Although I'm not a big fan of @L.J.R.'s approach, the example below extends his/her answer to gain support for tikz.

Notable improvements:

• By patching internal of \colorlet, it now supports tikz.
• Skipping patching when the color expression doesn't contain |.

\documentclass{article}
\usepackage{xpatch}
\usepackage{tikz}
\usepackage{tabularray}

\usepackage{unravel}
\unravelsetup{max-action=1000, max-input=1000, max-output=1000}
\long\def\beginunravel#1\endunravel{\unravel{#1}}
\providecommand\beginunravel{}
\def\endunravel{}

\makeatletter

% The following set of ugly patches based on
%   https://tex.stackexchange.com/a/629719
% extend xcolor <expr> (see `texdoc xcolor`, Table 4) to
%   <expr> ::= <mode> "|" <spec>
%            | <original expr>
% and add constraint that a (user-defined) color name must NOT contaion `|`

% for \color, \textcolor, etc.
\xpretocmd\@declaredcolor
  {\my@hack@definetempcolor{#1}}
  {}{\PatchFailed}

\def\my@hack@color{\xglobal\definecolor}

% for \colorlet (used by tikz)
\xpretocmd\XC@col@rlet
  {\my@hack@definetempcolor{#4}}
  {}{\PatchFailed}

% shared inner helper macros

% if color expression #1 contains `|` and is an undefined color name, execute
%   \xglobal\definecolor{#1}{<#1 pre |>}{<#1 post |>}
\def\my@hack@definetempcolor#1{%
  % a bit normalization: remove all spaces from #1
  \expanded{\my@hack@@definetempcolor{\zap@space#1 \@empty}}}%
\protected\def\my@hack@@definetempcolor#1{%
  \in@|{#1}%
  \ifin@
    \@ifundefinedcolor{#1}{\my@hack@splitcolor#1\@nil{\xglobal\definecolor}}{}%
  \fi
}

\def\my@hack@splitcolor#1|#2\@nil#3{#3{#1|#2}{#1}{#2}}
\makeatother

\begin{document}
{ \color{rgb|0.5,0.7,0.9}TEXT }

\textcolor{HTML|a65dbd}{TEXT}

\begin{tblr}{row{1} = {bg={HTML|11AA33}}}
  Alpha & Beta & Gamma
\end{tblr}

\tikz[line width=3pt]
  \draw[{HTML|a65dbd}, fill={rgb|0.5,0.7,0.9}] (0,0) rectangle (1,1);
\end{document}

Answer 2

At least the following dirty code works for tabularray package :-)

\documentclass{article}

\usepackage{xcolor}
\usepackage{etoolbox}
\usepackage{tikz}
\usepackage{tabularray}

\makeatletter
\ExplSyntaxOn

\pretocmd{\@declaredcolor}{\my@hack@color{#1}}{}{}

\def\my@hack@color#1{\@ifundefined{\@backslashchar color@#1}{\MyDefineColor{#1}}{\relax}}

\cs_generate_variant:Nn \seq_set_split:Nnn { Nnx }

\NewDocumentCommand \MyDefineColor { m } {
  \seq_set_split:Nnx \l_tmpa_seq {|} {#1}
  %\seq_show:N \l_tmpa_seq
  \exp_args:Nnxx \definecolor{#1} { \seq_item:Nn \l_tmpa_seq {1} } { \seq_item:Nn \l_tmpa_seq {2} }
}

\ExplSyntaxOff
\makeatother

\begin{document}

{ \color{rgb|0.5,0.7,0.9}TEXT }

\textcolor{HTML|a65dbd}{TEXT}

\begin{tblr}{row{1} = {bg={HTML|11AA33}}}
  Alpha & Beta & Gamma
\end{tblr}

%% This is not working:
%\tikz \path[draw={HTML|012acd}] (0,0) -- (1,1);

\end{document}

Answer 3

For tikz and packages based on it (and pgfkeys), the following new key handler /.raw color may help.

Usages:

• \draw[<color>] -> \draw[.raw color={<color model>}{<color spec>}]
• key=<color> -> key/.raw color={<color model>}{<color spec>}

To support \draw[<extended color spec>] and/or key=<extended color spec>, one has to patch several places of tikz, and maybe even pgf, which I doubt it's worth.

\documentclass{article}
\usepackage{tikz}
\usepackage{tcolorbox}

\makeatletter
\newcount\pgfutil@colorcnt

%   \pgfkeys{key/.raw color={rgb}{1,0,0}}
% is equivalent to
%   \definecolor{<name>}{rgb}{1,0,0}
%   \pgfkeys{key=<name>}
% where <name> is `pgf@color@rgb@1,0,0`
\pgfkeys{/handlers/.raw color/.code 2 args={%
  \expandafter\pgfkeys@rawcolor\expanded{{pgf@color@\pgfkeys@zap@space #1@#2 \@empty}}{#1}{#2}%
}}

% #1 = (internal) color name, #2 = color model, #3 = color spec
\def\pgfkeys@rawcolor#1#2#3{%
  \expandafter\xglobal % for efficiency concerns, define the color globally
                       % note \xglobal is provided by `xcolor`, hence importable
  \pgfutil@definecolor{#1}{#2}{#3}%
  \edef\pgf@expanded@path{\pgfkeyscurrentpath}% was `\the\pgfkeys@pathtoks`
  % Note `/tikz/<name>` is different from `tikz/.cd, <name>`. Only the latter 
  % will be directed to `/tikz/.unknown` hence parse color name correctly.
  \ifx\pgf@expanded@path\pgfkeys@defaultpath@tikz@text
    \pgfkeysalso{{#1}}%
  \else
    \pgfkeysalso{\pgfkeyscurrentpath={#1}}%
  \fi
}

% helper, the same as \zep@space in latex2e
\def\pgfkeys@zap@space#1 #2{%
  #1%
  \ifx#2\@empty\else\expandafter\pgfkeys@zap@space\fi
  #2}

\def\pgfkeys@defaultpath@tikz@text{/tikz}
\makeatother


\begin{document}
\begin{tikzpicture}[line width=2pt]
  \draw[red, fill=blue]
    (0,0) rectangle +(1,1) node[text=black!30] {node text};
  \draw[.raw color={rgb}{1,0,0}, fill/.raw color={HTML}{0000FF}]
    (2,0) rectangle +(1,1) node[text/.raw color={cmyk}{0,0,0,.3}] {node text};
\end{tikzpicture}

\tcbset{nobeforeafter}
\tcbox[colback=green!50]{tcbox content}\qquad
\tcbox[colback/.raw color={rgb}{.5,1,.5}]{tcbox content}
\end{document}

Answer 4

As I said, it also can be done with very simple tools: xcolor, cellspace and a tabular environment:

\documentclass[12pt]{article}
\usepackage[svgnames, table]{xcolor}
\usepackage{cellspace}
\setlength{\cellspacetoplimit}{18pt}
\setlength{\cellspacebottomlimit}{18pt}

\begin{document}

{\centering \Huge\bfseries
\begin{tabular}{llSl}
\color{PowderBlue} TEXT \\
\color{MediumOrchid} TEXT \\
\rowcolor{MediumSeaGreen!60!OliveDrab} \enspace Alpha\enspace &\enspace Beta\enspace &\enspace Gamma\enspace
\end{tabular}
}
\end{document}