Although perception begins when a stimulus is transduced by a sensory neuron, numerous perceptual mechanisms can modify sensory information as it is processed by an animal’s nervous system. One such mechanism is categorical perception, in which 1) continuously-varying stimuli are labelled as belonging to a discrete number of categories and 2) there is enhanced discrimination between stimuli from different categories as compared to equally-different stimuli from within the same category. We have shown previously that female zebra finches (Taeniopygia guttata) categorically perceive colours along an orange-red continuum that aligns with the carotenoid-based colouration of male beaks, a trait that serves as an assessment signal in female mate choice. Here we demonstrate that categorical perception occurs along a blue-green continuum as well, suggesting that categorical colour perception may be a general feature of zebra finch vision. Although we identified two categories in both the blue-green and the orange-red ranges, we also found that individuals could better differentiate colours from within the same category in the blue-green as compared to the orange-red range, indicative of less clear categorization in the blue-green range. We discuss reasons why categorical perception may vary across the visible spectrum, including the possibility that such differences are linked to the behavioural or ecological function of different colour ranges.