Most psychology students are familiar with the theories of colour vision that explain the perception of colour as being the product of activation of wavelength-specific cells in the retina, as well as opponent processes amongst ganglion cells further in the perceptual system. In many cases these models are correct – colour seems to be processed from the bottom up, based on wavelengths of light. However, top-down processing of colour information, where expectations influence colour perception, are also possible. In this activity we will explore top-down influences on colour perception.