Abstract
As Apple firstly launched iPhone in 2007, first generation of mobile devices rapidly raised using the same interface design approach establish by iOS Human Interface Guidelines that means skeuomorphysm. The interface of iOS and Android smartphones were 3D, bold, rounded, coloured, shaded and hyper-metaphorically similar to the real world. As always happened in design field, when something new is introduced into the market, it uses a mimetic approach with the already existing world so that people can easily create a mental model based on their previous experience. Colours were used in a natural way to convey a recognizable and reliable image of the world, so realistic to be transparent to the users perception. The enhancement in 2013 of iOS7 to flat design represent a significant breaking point. Quickly implemented and expanded as material design in a deeply well-structured Android manual, flat approach has significantly altered the use and the language of colours applied to graphical and touch interfaces both in mobile and desktop operating systems. On one and, material design introduces a wide, massive and bold use of colours so that they become one of the most powerful and expressive assets of the interaction and experience system. But, on the other hand, they assume a connotative and abstract role in identifying elements and in orientating the users across sections, navigations, call-to actions and feed-backs. Colours become unnatural, saturated, pop, acid. Contrast are strong and effective, but sometimes overwhelming. Moreover some of the established pattern, semiotic and cultural meanings – coming both from basic design and graphical user interfaces guide-lines – are disregarded. This sloppy and inconsistent use of colour language creates misunderstandings and errors in the users experience. The paper presents and discusses the main problems of colour design and usability mapping them in the three main mobile operating system - iOS, Android and Windows-Surface – critically comparing design guide-lines according to visual design principles and Gestalt Theory to suggest and improve a general review.