colortcolorbox
Imagine having a certain tcolorbox (manual) named FOO, called for via:
\documentclass{article}
\usepackage[most]{tcolorbox}
\newtcbox{\FOO}{colback=red,colframe=blue}
\begin{document}
\FOO{Something}
\FOO{Something else}
\end{document}
Now, is it possible to include something in the Preamble (i.e. before \begin{document}) such that every FOO will have e.g. green text?
These option clashes happen when a package is requested to be loaded on two different positions, like by you and inside another package, but with different options. The package is loaded by the first \usepackage (or its twin \RequirePackage); it isn't loaded again when it is requested again. It simply can't be loaded a second time. Therefore the new options can be activated and previous options might conflict with the second usage. So LaTeX creates an error to report this issue to you.
The way to fix this is to declare the options beforehand using \PassOptionsToPackage{<options>}{<package>}. Then they are used wherever the package is loaded.
\documentclass{article}
\usepackage{ifpdf}
\ifpdf
\PassOptionsToPackage{pdftex,usenames,dvipsnames}{color}
\usepackage[T1]{fontenc}
\usepackage{libertine} % most likely loads 'color' itself
%\usepackage{lmodern} % doesn't load 'color'
\usepackage{color}
\usepackage[pdftex]{graphicx}
\else
%\bye
\fi
\begin{document}
Hello, world!
\end{document}
I can't test it by myself, because I don't have the libertine package installed.
I don't think you need to set pdftex manually. Normally packages do a good job recognizing the driver by themselves. Also you might want to use the extended xcolor package instead of color.
With no warranty of any kind!
\documentclass{article}
\usepackage{color}
\makeatletter
\def\colorizemath #1#2{%
\expandafter\mathchardef\csname orig:math:#1\endcsname\mathcode`#1
\mathcode`#1="8000
\toks@\expandafter{\csname orig:math:#1\endcsname}%
\begingroup
\lccode`~=`#1
\lowercase{%
\endgroup
\edef~{{\noexpand\color{#2}\the\toks@}}}%
}
\@for\@tempa:=a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x,y,z\do{%
\expandafter\colorizemath\@tempa{green}}
\@for\@tempa:=A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z\do{%
\expandafter\colorizemath\@tempa{green}}
\@for\@tempa:=0,1,2,3,4,5,6,7,8,9\do{%
\expandafter\colorizemath\@tempa{red}}
\makeatother
\everymath{\color{blue}}
\everydisplay{\color{blue}}
\begin{document}\thispagestyle{empty}
Hello $world$. Do you know that $E=mc^2$?
\[ \widehat f(\omega) = \int_{-\infty}^\infty f(x) e^{-2\pi i \omega x}\,dx\]
\[ (I - M)^{-1} = \sum_{k=0}^\infty M^k\]
\end{document}
Let me add, with regards to \everymath and \everydisplay that it would have been better to do:
\everymath\expandafter{\the\everymath \color{blue}}
\everydisplay\expandafter{\the\everydisplay \color{blue}}
This preserves, rather than erases, the previously stored data in these token lists. (I just checked and Lamport's book does not have a single mention of token list, and even the word token is not to be found (it seems) in the entire book...). Admittedly, packages who put things in them should do that At Begin Document so even the brutal way used in my initial code, as long as it is in the preamble, is maybe not that destructive. People interested in token lists can learn about it in, for example, TeX by Topic by Victor Eijkhout (texdoc topic).
Best Answer
You can use
fontupperlikeIf you are using
\tcblowerthen there is also\fontlowerwhich will apply to the lower part. Here you can use font changing commands (like\sffamily) too in addition to colour commands.Equivalently you can use
colupper=greenandcollower=green. There is alsocoltextwhich should be used ascoltextis a short hand for using bothcolupperandcollower.