DCOLOR uses a coloring function to map the angle and modulus of complex data to color. This technique is known as domain coloring, and is an excellent tool to explore the behavior of complex-valued functions.
DCOLOR can produce plots using either a complex matrix or a function handle as the source data. There are several built-in coloring functions as well as the option to supply a user-defined coloring function as a function handle. Additionally, the 'grid' option can create contours of the real and imaginary parts of the complex data. See the help text for details and usage examples.
The following references have more information about visualizing complex-valued functions using domain coloring, including example images: