At present more than half of all building activity in the German building sector is undertaken within existing built contexts. Work in existing building fabric is an essential aspect of most architectsi activities. The development of a conceptual and technological basis for the digital support of design directly on site, in and with the available architecture is the main focus of the research project “Spatial Augmented Reality for Architecture”. This article describes one part of the research project: the sampling of colours and materials at a scale of 1:1 using Augmented Reality technologies. This makes it possible to project the colour and material qualities of a design directly onto any surface within an existing building, geometrically corrected. A first software prototype SAR-CA has been developed and then assessed using a user study to obtain a first evaluation of the prototype to determine the direction of future research. Future research areas are discussed at the end of the paper.