A slice plot is a neat way of displaying a 3D function f(x,y,z) in one plot. By default, three plots are made on top of each other, one in blue, one in green and one in red. Each of these surface plots are actually plots of the functions f(x,y,-1), f(x,y,0) and f(x,y,1). These three plots together should give a reasonable insight of what the whole function looks like.
Please note that complex outputs are plotted as their absolute value. These plots are only for indicative purposes throughout the modeling process. When modeling complex data, the phase IS modeled too, and can be retrieved (and plotted if wanted) by evaluating the stored models after the modeling process terminates.