How colour‐deficient observers see things, or not.

Colour deficiency or, colloquially, colour blindness, is common and has been observed and described in the scientific literature for ca . 200 years. In more recent times, algorithms have been developed that simulate the effect of colour deficiency to a colour‐normal observer. Sometimes these algorithms are used to indicate potential problems in the colour design, but often the implicit assumption is that a colour‐deficient observer actually sees things that way. But do they? This paper questions some of the underlying assumptions of the algorithms.