colortodonotes
Consider following MWE:
\documentclass{article}
\usepackage{blindtext}
\usepackage[colorinlistoftodos,prependcaption,textsize=tiny]{todonotes}
\presetkeys%
{todonotes}%
{inline,backgroundcolor=yellow,textcolor=blue!20!white}{}
\begin{document}
\blindtext\todo{Is this text in blue?}
\end{document}
How can I specify globally the textcolor of my todonotes?
Knuth in the TeXBook gave an example of "poor man's bold," (The TeXbook, p. 386) which can be typeset obtained by overprinting the normal weight symbol with slight offsets.
As he says:
The results are somewhat fuzzy, and they certainly are no match for the real thing if it's available; but poor man's bold is better than nothing, and once in a while you can get away with it.
Here, one can use a similar technique and the code is shown below:
\documentclass{article}
\usepackage{graphicx,xcolor}
\usepackage{amsmath}
\def\PoorManContour#1#2#3{\leavevmode
\setbox0=\hbox{{#1}}%
\color{#3}\kern-.002em\copy0\kern-\wd0
\color{#3}\raise-.04em\copy0\kern-\wd0
\color{#3}\lower.04em\copy0\kern-\wd0
\color{#3}\raise0.04em\copy0\kern-\wd0
\color{#2}\raise-.012em\copy0\kern-\wd0
\color{#2}\kern.06em\copy0\kern-\wd0
\color{blue}\kern-.020em\lower.003em\box0
}
\begin{document}
\colorbox{gray!5}{\scalebox{5}{\PoorManContour{$\sqrt{\dfrac{A^3_i}{B^2}}$}{gray!60}{gray!60}}}
\end{document}
To achieve the best results possible one has to kern in small steps for possibly twenty steps or so. For simplicity, I have not done that. In the final version, you need to adjust the colors to suit, possibly changing the shading to white.
Edit
After reading Jan's comment below I read the manual and true, as the commenter said the easiest way to achieve what the OP wanted is to include the package without an option i.e., \usepackage{contour}. Helps to RFM!
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.
Best Answer
You can specify text color via the style used for the nodes as follows: