# Package xcolor Error: Undefined color gold'

When I compile this document using pdflatex, my chapter's (and sections and subsections, too) titles are, respectively, blue (here defined as 'azzurro') and gold.

I would like that all titles and subtitles be black.

This is the document:

    \documentclass[envcountsame,envcountchap]{svmono}

%\usepackage[latin1]{inputenc}
\usepackage[utf8]{inputenc}
\usepackage{eurosym}
\usepackage{makeidx}                % allows index generation
\usepackage{graphicx}               % standard LaTeX graphics tool
\usepackage{xtab}                   % when including figure files
\usepackage{multicol}
\usepackage{qtree}
\usepackage{booktabs}
\usepackage{latexsym}
\usepackage{psfig}                  % used for the two-column index
\usepackage[bottom]{footmisc}       % places footnotes at page bottom
\usepackage[italian]{babel}
\usepackage{my_listings}
\usepackage[hyphens]{url}
\usepackage{algorithm}
\usepackage{algorithmic}
\usepackage{multirow}
\usepackage{xcolor}
\usepackage{float}
\usepackage{titlesec}
\usepackage{csquotes}
\usepackage{python}
\usepackage{verbatim}
\usepackage{eurosym}
\usepackage[figuresright]{rotating}
\usepackage{pdflscape}
\usepackage{tcolorbox}
%\setcounter{secnumdepth}{3}
%\setcounter{tocdepth}{3}
\makeatletter
\titleformat{\section}[display]%
{\Large\bfseries\boldmath}{\color{azzurro}{\thesection}}{-1.1em}{\hspace{2em}\color{azzurro}}[{\titlerule[0pt]}]
\makeatother

\makeatletter
\titleformat{\subsection}[display]%
{\large\bfseries\boldmath}{\color{gold}{\thesubsection}}{-1em}{\hspace{3em}\color{gold}}[{\titlerule[0pt]}]
\makeatother

\makeatletter
\titleformat{\subsubsection}[display]%
{\normalsize\bfseries\boldmath}{\color{gold}{\thesubsubsection}}{-1em}{\color{gold}}[{\titlerule[0pt]}]
\makeatother

\definecolor{gold}{rgb}{0.64,0.54,0.29}
\definecolor{azzurro}{rgb}{0,0.29,0.57}

\def\lstlistlistingname{\textbf{Elenco dei listati}}

\makeatletter
\let\old@rule\@rule
\def\@rule[#1]#2#3{\textcolor{gold}{\old@rule[#1]{#2}{#3}}}
\makeatother

\setlength{\textwidth}{12.7cm}
\setlength{\textheight}{20.0cm}
\setlength{\oddsidemargin}{3.50cm}
\setlength {\evensidemargin}{-0.3cm}
\setlength {\topmargin}{-1cm}

\makeindex

\author{}

\date{13 marzo 2018}

\begin{document}

\pagenumbering{{\color{azzurro}Roman}}
%\include{frontespizio/frontespizio}
%\newpage\null\thispagestyle{empty}\newpage
%\include{dedica/dedica}
%\tableofcontents \listoffigures
%\lstlistoflistings

\pagenumbering{arabic} \setcounter{page}{1}

%\include{Introduzione/introduzione}
\include{01-IlCrowdsourcing/capitolo-01}
%\include{02-LaSentimentAnalysis/capitolo-02}
%\include{07-ConfrontoConApprocciCorrelati/capitolo-07}
%\include{08-DiscussioneInMeritoAll'attivitàSvolta/capitolo-08}

\nocite{*}
%\bibliography{Bibliografia/biblio}
\bibliographystyle{plain}
%\include{Ringraziamenti/ringraziamenti}
\end{document}


In this way the file is compiled like the attached image.

When I replace the colors with 'black' as

\definecolor{black}{rgb}{0,0,0}


it give me these errors:

Package xcolor Error: Undefined color gold

Package xcolor Error: Undefined color azzurro

What I can do?

Observe that you are using \color{azzurro} (twice: one for counter and other for title) in the definition of \subsection.

\makeatletter
\titleformat{\section}[display]%
{\Large\bfseries\boldmath}{\color{azzurro}{\thesection}}{-1.1em}{\hspace{2em}\color{azzurro}}[{\titlerule[0pt]}]
\makeatother


So just replace azurro by black or even better delete \color{azzurro}, since black is the default color.

Do the same in the definition of \subsection.

A bad but faster solution would be to keep the definitions and just change RGB values to the color namedazurro, ie, \definecolor{azzurro}{rgb}{0,0,0}. With that you will get a black azurro.

Finally, the error Package xcolor Error: Undefined color gold you got was because you had changed the name of the defined color (gold by black) but you were still using the gold` color in codes above. This is why undefined color error.