Custom citation (coloured) for select keys only

Question

Is there any way, using biblatex, to get citations for certain bib-keys / bib-entries, and only them, to be differently coloured?

In the MWE below, I've made a custom command (inspired by this answer) for differently coloured citations. However, what I am looking for is a way of having biblatex/biber automatically colour citations referencing certain entries, and only them, without using any custom commands. In the text, the same command would be used (e.g. \parencite) but for specified entries (e.g. articlecoloured) the output would be coloured; for other entries, it would not.

In other words, using the citation commands as in section "No custom commands" in the MWE but getting the same output as in section "Using custom commands".

The example includes a bib-content with two entries, articlenormal and articlecoloured.

I'd like to be able to use the normal citation commands (\parencite, \citeyear, \textcite etc.) but for some bib-keys (articlecoloured) output would be coloured; for all others (e.g. articlenormal) it would not. (In my working document, I have custom commands for the various citation commands I use, which all colour output as in the MWE. In the MWE, I've only included \parencite.)

Is it possible to get articlecoloured, and only articlecoloured, to have a custom colour without using a custom citation command?

Perhaps which bibentries to colour could be based either on a list of keys (i.e. articlecoloured), or to have a relevant keyword in the bibentry?

(Bonus points if specified entry to be coloured is also coloured in the bibliography.)

\documentclass{article}

\usepackage{xcolor} 
\definecolor{citecolor}{RGB}{12,127,172}

\begin{filecontents*}{mybib.bib}
@ARTICLE{articlenormal,
    author = {Normal, Article},
    title = {Normal},
    year = {2020}
}
@ARTICLE{articlecoloured,
    author = {Coloured, Article},
    title = {Coloured},
    year = {2020}
}
\end{filecontents*}

\usepackage[style=apa,backend=biber]{biblatex}
\DeclareLanguageMapping{english}{british-apa}

\bibliography{mybib}

% Using custom command
\newcommand{\mkbibparenscoloured}[1]{\textcolor{citecolor}{\mkbibparens{#1}}}

\DeclareDelimFormat[parencite]{finalnamedelim}
  {\ifnum\value{liststop}>2 \finalandcomma\fi\addspace\&\space}

\DeclareCiteCommand{\colparencite}[\mkbibparenscoloured]
  {\usebibmacro{cite:init}%
   \usebibmacro{prenote}%
   \toggletrue{apa:inpcite}}
  {\usebibmacro{citeindex}%
   \usebibmacro{cite}%
   \usebibmacro{cite:post}}
  {}
  {\usebibmacro{postnote}%
   \togglefalse{apa:inpcite}}

\begin{document}

\section*{No custom commands}

Citation, should be normal colour \parencite{articlenormal}.

Citation, should be differently coloured \parencite{articlecoloured}.

\section*{Using custom commands}

Citation, should be normal colour \parencite{articlenormal}.

Citation, should be differently coloured \colparencite{articlecoloured}.

\printbibliography{}

\end{document}

Answer 1

Essentially we 'just' need to take the original definition of the cite and textcite bibmacros and sprinkle some colour in there.

The original definitions can be found in apa.cbx (ll. 189-261 in v9.6).

In this example you can define which citations are going to be coloured with

\addtocategory{coloured}{<key_1,key_2,...,key_n>}

so this is useful if the entry is only coloured in the context of a certain document and not in and of itself.

\documentclass{article}
\usepackage{xcolor}
\definecolor{citecolour}{RGB}{12,127,172}

\usepackage[style=apa,backend=biber]{biblatex}

\DeclareBibliographyCategory{coloured}
\addtocategory{coloured}{articlecoloured}

\DeclareFieldFormat{citecolour:conditional}{%
  \ifcategory{coloured}
    {\textcolor{citecolour}{#1}}
    {#1}}

\makeatletter
\renewbibmacro*{cite}{%
  \iffieldequals{fullhash}{\cbx@lasthash}
   {\setunit{\compcitedelim}%
    \printtext[citecolour:conditional]{%
      \usebibmacro{cite:plabelyear+extradate}}}%
   {\printtext[citecolour:conditional]{%
      \ifnameundef{labelname}
       {\usebibmacro{cite:noname}%
         \setunit{\printdelim{nameyeardelim}}%
         \usebibmacro{cite:plabelyear+extradate}%
         \savefield{fullhash}{\cbx@lasthash}}
       {\ifnameundef{shortauthor}
         {\printnames{labelname}}%
         {\cbx@apa@ifnamesaved
           {\printnames{shortauthor}}
           {\ifnameundef{groupauthor}
             {\printnames[labelname]{author}}
             {\printnames[labelname]{groupauthor}}%
            \addspace\printnames[sabrackets]{shortauthor}}}%
         \setunit{\printdelim{nameyeardelim}}%
        \usebibmacro{cite:plabelyear+extradate}%
        \savefield{fullhash}{\cbx@lasthash}}}}%
   \setunit{\multicitedelim}}

\renewbibmacro*{textcite}{%
  \iffieldequals{fullhash}{\cbx@lasthash}
    {\setunit{\compcitedelim}%
     \printtext[citecolour:conditional]{%
       \usebibmacro{cite:plabelyear+extradate}}}
    {%
    \ifbool{cbx:parens}
      {\bibcloseparen\global\boolfalse{cbx:parens}}
      {}%
      \setunit{\compcitedelim}%
      \ifnameundef{labelname}
       {\iffieldundef{shorthand}%
         {\printtext[citecolour:conditional]{%
            \usebibmacro{cite:noname}}%
          \setunit{\ifbool{cbx:np}%
                   {\printdelim{nameyeardelim}}%
                   {\global\booltrue{cbx:parens}\addspace\bibopenparen}}%
          \printtext[citecolour:conditional]{%
            \usebibmacro{cite:plabelyear+extradate}}}
         {\printtext[citecolour:conditional]{%
            \usebibmacro{cite:shorthand}}}}
       {\printtext[citecolour:conditional]{%
          \ifnameundef{shortauthor}%
           {\printnames{labelname}}
           {\cbx@apa@ifnamesaved
             {\printnames{shortauthor}}
             {\ifnameundef{groupauthor}
               {\printnames[labelname]{author}}
               {\printnames[labelname]{groupauthor}}}}}%
        \setunit{\ifbool{cbx:np}
                  {\printdelim{nameyeardelim}}
                  {\global\booltrue{cbx:parens}\addspace\bibopenparen}}%
        \printtext[citecolour:conditional]{%
          \ifnameundef{shortauthor}
           {}
           {\cbx@apa@ifnamesaved
             {}
             {\printnames{shortauthor}\setunit{\printdelim{nameyeardelim}}}}%
          \usebibmacro{cite:plabelyear+extradate}}%
        \savefield{fullhash}{\cbx@lasthash}}}}

\DeclareCiteCommand{\fullcite}
  {\usebibmacro{prenote}}
  {\usedriver
    {\ifcategory{coloured}
       {\color{citecolour}}
       {}%
      \DeclareNameAlias{sortname}{default}%
      \global\boolfalse{bbx:in}%
      \global\let\blx@related@loop\@empty}
    {\thefield{entrytype}}%
   \usebibmacro{cite:post}}
  {\multicitedelim}
  {\usebibmacro{postnote}}

\DeclareCiteCommand{\fullcitebib}
  {\list{}
   {\setlength{\leftmargin}{\bibhang}%
     \setlength{\itemindent}{-\leftmargin}%
     \setlength{\itemsep}{\bibitemsep}%
     \setlength{\parsep}{\bibparsep}}\item}
  {\usedriver
    {\ifcategory{coloured}
       {\color{citecolour}}
       {}%
      \DeclareNameAlias{sortname}{default}%
      \global\boolfalse{bbx:in}}
    {\thefield{entrytype}}%
   \finentry
   \usebibmacro{cite:post}}
  {\item}
  {\endlist}
\makeatother

% for the bibliography
\AtEveryBibitem{%
  \ifcategory{coloured}
    {\color{citecolour}}
    {}}

\begin{filecontents*}{\jobname.bib}
@article{articlenormal,
    author = {Normal, Article},
    title  = {Normal},
    year   = {2020},
}
@article{articlecoloured,
    author = {Coloured, Article},
    title  = {Coloured},
    year   = {2020},
}
\end{filecontents*}
\addbibresource{\jobname.bib}

\begin{document}
Citation, should be normal colour \parencite{articlenormal}.

Citation, should be differently coloured \parencite{articlecoloured}.

Citation, should be normal colour \textcite{articlenormal}.

Citation, should be differently coloured \textcite{articlecoloured}.

\printbibliography
\end{document}

---

If the entry is coloured by its very nature, it would be more natural to work with keyowrds

Simply replace the

\ifcategory{coloured}

above with

\ifkeyword{coloured}

and mark coloured entries up with

keywords = {coloured},

in the .bib file.