[Matplotlib-users] continous colormap with 'plateau'

Hi everyone,

is it possible to map a certain range within the value-range of a image plot to 
a constant value? Currently I am overlaying a filled contour plot with just two 
contour levels on top of an image plot. This works, but I would like to display 
the plateau in the colorbar as well, so that the color changes continously over 
the whole value range but in the specified range where it should remain white. 
I guess I would need a special colormapper to achieve that.

Thanks in advance for any pointers, Christian