Dichromatic colour vision is commonly believed to be a reduced form of trichromatic colour vision (referred to as the reductionist principle). In particular, the colour palette of the dichromats is believed to be a part of the colour palette of the trichromats. As the light-colour palette differs from the object-colour palette, the dichromatic colour palettes have been derived separately for light-colours and object-colours in this report. As to light-colours, the results are in line with the widely accepted view that the dichromatic colour palettes contain only two hues. However, the dichromatic object-colour palettes have proved to contain the same six component colours which constitute the trichromatic object-colour palette (yellow, blue, red, green, black and white). Moreover, all the binary and tertiary combinations of the six component colours present in the trichromatic object-colour palette also occur in the dichromatic object-colour palettes. Yet, only five of the six component colours are experienced by dichromats as unitary (unique) object-colours. The green unitary colour is absent in the dichromatic object-colour palettes. The difference between the dichromatic and trichromatic object-colour palettes arises from the fact that not every combination of the component-colour magnitudes occurs in the dichromatic object-colour palettes. For instance, in the dichromatic object-colour palettes there is no colour with the strong green component colour. Furthermore, each achromatic (black or white) component colour of a particular magnitude is combined with the only combination of the chromatic components. In other words, the achromatic component colours are bound with the chromatic component combinations in dichromats. (c) 2012 Wiley Periodicals, Inc.