Over the past decade or so, interference effect pigments have evolved from simple single crystals or simple coated substrates to advanced multilayer optical structures. These advanced structures have led to enhanced optical properties such as high chroma and colour travel. In contrast to a simple interference pigment with only one optical layer, in multilayer optical structures all the layers work together to create the resultant interference. To understand how these multilayer interference effect pigments work and how to design them, it is important to understand the optics behind them. Early generations of effect pigments ...