PCOLOR Pseudocolor Plot
Section:  Handle-Based Graphics 
Usage
This routine is used to create a pseudocolor plot of the data.
A pseudocolor plot is a essentially a surface plot seen from 
above.  There are two forms for the pcolor command:
   pcolor(C)
which uses a rectangular grid.  Alternately, you can specify
X,Y matrices or vectors.
   pcolor(X,Y,C)