Building complex materials with structures on a scale comparable to the wavelength of light offers possibilities for radically changing the way light moves around such materials, in the same way that we engineer atomic structure to vary electronic properties of semiconductors. In this paper we describe in detail how to make numerical calculations of the dispersion relations (the band structure) of these complex objects, and how to calculate transmission through, and reflection from them. Finally these methodologies are applied to a colloidal dispersion of metallic particles at 12% volume filling fraction to reproduce the well known characteristics of strong optical absorption.