Colons e.g. in \definecolor{⋯}{rgb:Hsb}{⋯} not allowed between \ExplSyntaxOn/\ExplSyntaxOff

[dbitouze]

(Original report here.)

The following MCE:

% \RequirePackage{pdfmanagement-testphase}
% \DeclareDocumentMetadata{}
\documentclass{article}
\usepackage{xcolor}
\ExplSyntaxOn
\definecolor{blue3}{rgb:Hsb}{240,0.67,0.70}
\ExplSyntaxOff
\begin{document}
Test.
\end{document}

compiles like a charm but, as soon as the two first lines are commented out, throws the error:

! LaTeX3 Error: Unknown color model 'rgb:Hsb'.

For immediate help type H .
...

l.6 \definecolor{blue3}{rgb:Hsb}{240,0.67,0.70}

[u-fischer]

looks like a l3color problem. The docu says To allow parsing of data from xcolor, any leading model up the first : will be discarded; the approach of selecting an internal form for data is not used in l3color., but actually it doesn't work if the colon has catcode letter:

\documentclass{article}
\ExplSyntaxOn
%\color_set:nnn{test}{rgb:Hsb}{240,0.67,0.70} %fails
\exp_args:Nnx
\color_set:nnn{test}{rgb\c_colon_str Hsb}{240,0.67,0.70}
\color_show:n{test}
\ExplSyntaxOff
\begin{document}
blub
\end{document}

@josephwright what do you think?

[josephwright]

I guess I'd been thinking of colons here as document-level syntax: I'll look to fix.

[lvjr]

There is a similar problem here: https://tex.stackexchange.com/questions/614621/tabularray-and-rgb-xcolor-option

Is it a bug of xcolor or my wrong usage of xcolor package in ninecolors package?

If it is the former, should I open an issue at https://github.com/latex3/xcolor/issues?

[u-fischer]

@lvjr This bug here has been resolved. Your problem is another one I opened an issue about it in the xcolor repo. But at a first glance it is not trivial to sort out, so it would be better if you defined your colors in a simpler way, e.g. convert them first.

[davidcarlisle]

@lvjr Ulrike just opened latex3/xcolor#1