As mentionned in Martin's comment, the trick is to draw the line twice. One of the constraints on paths in Tikz/PGF is that the color is global to the path.
Other than drawing a solid line covered by a dashed line, you may draw two dashed lines, with spaces between the dashes, as given by the following example (you can find more information in the Tikz manual) :
\begin{tikzpicture}
\draw[blue,dash pattern= on 3pt off 5pt] (0,0) |- (1,1) to[out=0,in=90] (2,0);
\draw[red,dash pattern= on 3pt off 5pt,dash phase=4pt] (0,0) |- (1,1) to[out=0,in=90] (2,0);
\end{tikzpicture}
The outcome is
(Following a comment by Caramdir) : The same result can be achieved with a postaction, and the path only has to be specified once :
\draw[postaction={draw,red,dash pattern= on 3pt off 5pt,dash phase=4pt,thick}]
[blue,dash pattern= on 3pt off 5pt,thick] (0,0) |- (1,1) to[out=0,in=90] (2,0);
(Following a request for a rectangle) * I'm not sure this answers the question in the comment *
For a rectangle you would type in the command
\draw[postaction={draw,red,dash pattern= on 3pt off 5pt,dash phase=4pt,thick}]
[blue,dash pattern= on 3pt off 5pt,thick] (0,0) rectangle (3,2);
This rectangle does not have rounded corners, it is a "normal" rectangle. If ever you do want rounded corners, add rounded corners to the options :
\draw[postaction={draw,red,dash pattern= on 3pt off 5pt,dash phase=4pt,thick,rounded corners}]
[blue,dash pattern= on 3pt off 5pt,thick,rounded corners] (0,0) rectangle (3,2);
A slightly different way is described in the following code. Note that you don't really need xcolor for this. Two tikz pictures are drawn, one using xcolor, the other using the basic commands in tikz. I drew the chain horizontally to save on space. I also added a macro that let's you change the number of nodes.
\documentclass{minimal}
\usepackage[rgb]{xcolor}
\usepackage{tikz}
\usetikzlibrary{chains}
\begin{document}
%with xcolor
\begin{tikzpicture}[start chain=chroma going right,
node distance = 2mm,
every node/.style ={shape=rectangle,minimum size =1cm,on chain}]
\pgfmathsetmacro{\nbnodes}{8}
\pgfmathsetmacro{\factor}{1/\nbnodes}
\foreach \n [evaluate=\n as \value using 1-\factor*\n] in {0,...,\nbnodes}{
\pgfmathsetmacro{\bordershade}{ifthenelse(\n==0,100,0)}
\definecolor{tmpc}{Hsb}{0,0,\value}
\node[draw=black!\bordershade,fill=tmpc] {};
}
\end{tikzpicture}
%without xcolor
\begin{tikzpicture}[start chain=chroma going right,
node distance = 2mm,
every node/.style ={shape=rectangle,minimum size =1cm,on chain}]
\pgfmathsetmacro{\nbnodes}{8}
\pgfmathsetmacro{\factor}{100/\nbnodes}
\foreach \n [evaluate=\n as \shade using \factor*\n] in {0,...,\nbnodes}{
\pgfmathsetmacro{\bordershade}{ifthenelse(\n==0,100,0)}
\node[draw=black!\bordershade,fill=black!\shade] {};
}
\end{tikzpicture}
\end{document}
The output is
Best Answer
You can define your own parameterized style to do this, with
Complete example:
The two nodes are identical: