add colors to scatter plots

I am simulating the movement of some particles that carry some
concentration of different species. Those concentrations change in time
and space and I would like to be able to see their distribution in

I am using the scatter plot of Matplotlib to plot the position of each
particle. That works great, but when I try to assign different colors to
each dot according to their concentration I find some problems. Although
there is a big range of concentrations (colors) I can only see two in
the plot. Is it possible to define more intervals to assign the colors?
I think I did not understand the right way to define the c array
intensities when I use the command:
scatter(self, x, y, s=None, c)
How should I generate that array? I looked at the example but I couldn't
figure it out.

Thanks for your help,
I look forward to see the future versions of Matplotlib. So far, it
looks very good.