In colour science and imaging, a remarkable range of understandings and technologies have been provided in recent years. But common practices in some areas operate as if certain of these ‘knowns’ are ‘unknown’. In colour science, examples include the following. The continued widespread use of the x,y chromaticity diagram instead of the more uniform u',v' diagram leads to serious distortions of the facts, particularly in regard to colour gamuts. An undue emphasis on colour constancy ignores the fact that, because of metamerism, and in the case of purples because of the inherent nature of their spectral properties, colour constancy fails significantly. The availability of the terms saturation, chroma, and colourfulness, makes possible proper consideration of the chromatic components of colour appearance; but the distinctions between these terms is often ignored. In imaging, examples of ‘knowns’ being treated as ‘unknowns’ include the following. Geometrical distortions caused by not treating 4:3 and 16:9 aspect ratios differently. The degradation of colour rendering by using a white primary in addition to red, green, and blue primaries in digital projectors. The use of linear plots of input and output in electronic imaging resulting in confusing terminology. The effects of viewing conditions and luminance-level on colour appearance being ignored because of the neglect of colour appearance models. The moral of all this is that, for those involved in colour science and imaging, it is not enough to provide knowledge and technologies; unless there is also adequate education in these areas, much of the intended benefits will be lost.