How can display overlaying lines as darker? Using for lines for density plot

In short, I would like to produce a plot as shown below. The problem is when I plot multiple lines, their colour stays the same. So two overlaying lines will have the colour of the top line, instead I would like to have these lines displayed as darker. Is there a way to do this in matlab.

I am open to suggestion of alternatives plots for pdf's along a line.

Any help would be greatly appreciated.

Answer 1

[Azzi Abdelmalek]

Look at Matt's answer http://www.mathworks.com/matlabcentral/answers/6056#answer_8420

[John]

cheers, this works well.

Answer 2

[Image Analyst]

Why not simply store all those curves into a 2-D array, and then take the mean vertically:

meanCurve = mean(allCurves, 1);

Or you could use the median instead of the mean.