This study corroborates the view that perceptual categorization does not require linguistic categories, and simple tasks like ordering colours on the basis of their similarities evince well-structured perceptual categories, defined relatively to visual perception and independently from experience, language and higher-level cognition. The independence of these categories from experience, language, and higher-level cognition would be an argument for their naturalness, and hence for their universality, and for their role in shaping language itself. On the other hand, the influence of language on colour perception would come about by facilitating perception-controlled behaviours. The ordering procedure which rests on perceptual similarity yields a colour system in which perceptual categories are implicit and yet clear and stable. In fact, it shows that whatever speakers in whatever language community share the same experience of colour. The arguments presented favour the 'universalist' thesis and are important in regard to both the research methodology and interpretation of the experimental data. The study's distinctive features are the interdisciplinary nature of its approach, the gestaltist theoretical and methodological conception adopted, and the concept of the naturalness of colour advanced and discussed.