Well, I found out how to shade. It is possible to define the colors you want to show in your figure by customizing the 'colormap' for example: black & white presentation of a contour figure:
colormap([1 1 1];[0 0 0])
if you want do divide the the weight of the colors:
colormap([1 1 1];[1 1 1];[1 1 1];[0 0 0])
Hope it will be of use.
and to all matlab begginers like me: You dug, you found. believe.