Quite good summary read on Interaction design Fundation about ‘The building blocks of visual design’.
‘Visual design is about creating and making the general aesthetics of a product consistent. To create the aesthetic style of a website or app, we work with fundamental elements of visual design, arranging them according to principles of design. These elements and principles together form the building blocks of visual design, and a firm understanding of them is crucial in creating a visual design of any product.’