Fading a path in TikZ

Question

I want to draw a path/plot in TikZ whose shade depends on the coordinate. For example, I want say something like

\draw[color=black!\x] plot coordinates{ coord1 ... coord100};

i.e. the shade of the color depends on the coordinate of the point. In examples of using colour in TikZ documention that I found, the colour is set for the entire path, and does not change with the point. Is there a way to do what I want?

Answer 1

The manual contains also the following example (first page of Part VII):

\pgfmathsetseed{1}
\foreach \col in {black,red,green,blue}
{
\begin{tikzpicture}[x=10pt,y=10pt,ultra thick,baseline,line cap=round]
\coordinate (current point) at (0,0);
\coordinate (old velocity) at (0,0);
\coordinate (new velocity) at (rand,rand);
\foreach \i in {0,1,...,100}
{
\draw[\col!\i] (current point)
.. controls ++([scale=-1]old velocity) and
++(new velocity) .. ++(rand,rand)
coordinate (current point);
\coordinate (old velocity) at (new velocity);
\coordinate (new velocity) at (rand,rand);
}
\end{tikzpicture}
}

This might give you an idea how to do it.