The notext option of the crop package removes all text for a similar purpose, e.g. that color graphics only can be printed with a color printer. (It has also a nographics option.)
It turns the color to white and disables all color macros to avoid the switching to different colors afterwards.
You have to save and later restore these commands inside the figure like shown below to get normal colors inside the figures. This works fine in my test.
\documentclass{article}
\usepackage{tikz}
% Save away the color command incl. their internal macros:
\let\origcolor\color
\expandafter\let\csname origcolor \expandafter\endcsname\csname color \endcsname
\let\origtextcolor\textcolor
\expandafter\let\csname origtextcolor \expandafter\endcsname\csname textcolor \endcsname
% there is also `\pagecolor` but it isn't of relevance here
\newcommand{\restorecolorcmds}{%
\let\color\origcolor
\expandafter\let\csname color \expandafter\endcsname\csname origcolor \endcsname
\let\textcolor\origtextcolor
\expandafter\let\csname textcolor \expandafter\endcsname\csname origtextcolor \endcsname
\color{black}%
}
\usepackage[notext]{crop}% must be after tikz
\usepackage{lipsum}% dummy text
\begin{document}
\lipsum
\begin{figure}
\restorecolorcmds
\centering
\begin{tikzpicture}
\draw (0,0) -- (1,1);
\draw [blue] (1,0) -- (0,1);
\end{tikzpicture}
\caption{caption text}
\end{figure}
\lipsum
\begin{figure}
\restorecolorcmds
\centering
\includegraphics[width=.8\textwidth]{image}
\caption{caption text}
\end{figure}
\lipsum
\end{document}
Update:
The solution can be easier and nicer coded using the etoolbox package, which also allows to automatically add the required macro to all figures and tables.
\documentclass{article}
\usepackage{tikz}
\usepackage{etoolbox}
% Save away the color command incl. their internal macros:
\let\origcolor\color
\csletcs{origcolor }{color }
\let\origtextcolor\textcolor
\csletcs{origtextcolor }{textcolor }
\csletcs{origdefault@color}{default@color}
% there is also `\pagecolor` but it isn't of relevance here
\newcommand{\restorecolorcmds}{%
\let\color\origcolor
\csletcs{color }{origcolor }%
\let\textcolor\origtextcolor
\csletcs{textcolor }{origtextcolor }%
\def\normalcolor{\origcolor{black}}%
\normalcolor
}
\AtBeginEnvironment{figure}{\restorecolorcmds}
\AtBeginEnvironment{table}{\restorecolorcmds}
\usepackage[notext]{crop}% must be after tikz
\usepackage{lipsum}% dummy text
\begin{document}
\lipsum
\begin{figure}
\centering
\begin{tikzpicture}
\draw (0,0) -- (1,1);
\draw [blue] (1,0) -- (0,1);
\end{tikzpicture}
\caption{caption text}
\end{figure}
\lipsum
\begin{figure}
\centering
\includegraphics[width=.8\textwidth]{image}
\caption{caption text}
\end{figure}
\lipsum
\end{document}