The package xcolor can "prepare" color definitions in such a way that they're only loaded if they're actually needed, which may be indicated by a later call to e.g. \providecolors{<id-list>}.
The package also has convenient commands to define a large set of colors sharing a common prefix/suffix: \preparecolorset{HTML}{<prefix>}{<suffix>}{red,ff0000;blue,0000ff} prepares colors <prefix>red<suffix> and <prefix>blue<suffix>.
These colors could then be loaded by calling \providecolors{<prefix>red<suffix>,<prefix>blue<suffix>}.
I'm trying to implement a convenience command to avoid having to repeatedly write out the shared prefix and suffix of the colors. The syntax would be \ProvideColorsFromSet{<prefix>}{<suffix>}{<list>}.
However, the code below, which I thought was rather simple, throws errors Undefined color 'my-red' and Undefined color 'my-blue'.
I'm guessing the problem's to do with expansion, so I've tried different combinations of \exp_args:... and \exp_not:... (without really knowing what I'm doing), but to no avail. I also tried to convert the clist to a seq, and to use \..._map_function instead of \..._map_inline, but with no success.
Any help would be much appreciated. Thank you!
\documentclass{article} \usepackage{xparse} \usepackage{xcolor} \definecolorsfalse \preparecolorset{HTML}{my-}{}{red,ff0000;blue,0000ff} \ExplSyntaxOn \NewDocumentCommand { \ProvideColorsFromSet } { m m m } { \clist_set:Nn \l_tmpa_clist { #3 } % \exp_args:NNx \clist_set:Nn \l_tmpa_clist { #3 } % \clist_set:Nn \l_tmpa_clist { \exp_not:n #3 } \clist_map_inline:Nn \l_tmpa_clist { #1##1#2 } \tl_set:Nn \l_tmpa_tl { \clist_use:Nn \l_tmpa_clist {,} } \providecolors{ \tl_use:N \l_tmpa_tl } % \exp_args:NV \providecolors{ \l_tmpa_tl } % \providecolors{ \l_tmpa_tl } % \providecolors{ \exp_not:N \l_tmpa_tl } % \providecolors{ \exp_args:NV \exp_not:N \l_tmpa_tl } % hmm... % \exp_args:Nx \providecolors{ \l_tmpa_tl } % \exp_args:Nx \providecolors{ \tl_use:N \l_tmpa_tl } } \ExplSyntaxOff \ProvideColorsFromSet{my-}{}{red,blue} \begin{document} \textcolor{my-red}{red} \textcolor{my-blue}{blue} \end{document} Addendum:
Definition of \providecolors in xcolor:
\def\XC@preparec@lor[#1]#2[#3]#4#5% {\XC@sdef\@@cls{#1}\XC@edef\@@nam{#2}% \XC@getmodclr01{#4}{#5}{}% {\xdef\XC@@stack {\ifx\XC@@stack\@empty\else\XC@@stack,\fi{#1}{\@@nam}{#3}% {\ifx\@@Mod\XC@mod@ignore\@@mod\else\@@Mod\fi}{\@@clr}}}} \let\XC@@stack\@empty \def\XC@definecolors#1,% {\@ifxempty{#1}{}{\expandafter\XC@definec@lors#1=#1=:\XC@definecolors}} \def\XC@definec@lors#1=#2=#3:% {\XC@edef\@@nam{#1}\XC@edef\@@arg{#2}% \let\next\XC@definec@l@rs\expandafter\next\XC@@stack,,\@nnil} \def\XC@definec@l@rs#1,% {\ifx,#1,\let\next\remove@to@nnil\else\XC@defin@c@l@rs#1\fi\next} \def\XC@defin@c@l@rs#1#2#3#4#5% {\def\@@tmp{#2}% \ifx\@@tmp\@@arg \let\xglobal@\XC@@glb\XC@@cmd[#1]{\@@nam}[#3]{#4}{#5}% \let\next\remove@to@nnil \fi} \def\providecolors#1% {\let\XC@@cmd\providecolor\let\XC@@glb\xglobal@ \expandafter\XC@definecolors#1,,} 
