Ok, looks like you've got your volumetric plots going. It's easy from here.
First, to display a color scale, the command is
Second, to explain how to get rid of the black lines you've got to understand something called handles. MATLAB represents its graphics in a series of nested structures called graphics handles. When you create a plot object you can usually assign the output to a variable. That will assign that variable the handle of that object. You can then interrogate the properties of that object by using the 'get' command. You can 'set' properties to change them. I recommend looking at the halp for more detail. However, for your case, it's just going to be:
h = slice(X,Y,Z,V,Sx,Sy,Sz);