The LaTeX2e kernel defines usepackage to be exactly the same as RequirePackage in the ltclass.dtx.
\if@compatibility\else\let\usepackage\RequirePackage\fi
So the fact that you use RequirePackage makes no difference and you still get an error. If the same package is requested more than
once, nothing happens, unless the package has been requested with options that
were not given the first time it was loaded, in which case an error is produced.
Once you get the error message:
! LaTeX Error: Option clash for package xcolor.
See the LaTeX manual or LaTeX Companion for explanation.
Type H <return> for immediate help.
...
l.17
type "h" (without the quotation marks, for help) in the output console and you get
? h
The package xcolor has already been loaded with options:
[]
There has now been an attempt to load it with options
[table]
Adding the global options:
,table
to your \documentclass declaration may fix this.
So, you get an explanation of the problem and a possible solution. Doing as advised you prevent the clash:
\documentclass[a4paper,oneside,article,table]{memoir}
\usepackage[latin1]{inputenc}
\usepackage[T1]{fontenc}
\usepackage[danish]{babel}
\usepackage{lmodern}
\usepackage{graphicx}
\graphicspath{{Figures/}}
\usepackage{fullpage}
\usepackage{modroman}
\usepackage{float}
\usepackage{caption}
\usepackage[numbers]{natbib}
\usepackage{url}
\usepackage{pgfplots}
\usepackage{mathtools}
\usepackage{xcolor}
\begin{document}
test
\end{document}
Now, the problem was that another package (pgfplots, in this case) had already loaded the xcolor package without options, so loading it after pgfplots with the table option produces the clash. One way to prevent the problem was already presented (using table as class option); another solution is to load xcolor with the table option before pgfplots:
\documentclass[a4paper,oneside,article]{memoir}
\usepackage[latin1]{inputenc}
\usepackage[T1]{fontenc}
\usepackage[danish]{babel}
\usepackage{lmodern}
\usepackage{graphicx}
\graphicspath{{Figures/}}
\usepackage{fullpage}
\usepackage{modroman}
\usepackage{float}
\usepackage{caption}
\usepackage[numbers]{natbib}
\usepackage{url}
\usepackage[table]{xcolor}
\usepackage{pgfplots}
\usepackage{mathtools}
\begin{document}
test
\end{document}
Best Answer
In an ideal world, the LaTeX message
Option clash for package …simply indicates an error and, as such, should not be ignored, but entail appropriate measures. Nonetheless, I’ve made the experience that, in reality, there are situations where it is either harmless or even advantageous to circumvent this error. Versatile tools for this purpose are\PreventPackageFromLoadingand\ResetPreventPackageFromLoadingfrom thescrlfilepackage. Minimal example: