A remarkable part of the diagnostic criteria in Dermatology is based on the colours of the skin lesions, their linear topography and the morphologic evaluation of the figures that the same lesions tend to develop. The process of visual analysis is an unconscious and routine mechanism in the clinical diagnostic activity of any Dermatologist. We first observe the colour, then the linear distribution and the shapes of the skin disorders. At this point we often make the diagnosis without little help of further investigation.