In the commercial paint industry, differences in application methods can lead to what is known as the “touch-up problem”, where two regions coated with exactly the same paint look different in color, gloss, or texture. In this paper we investigate the causes of the touch-up problem and identify physical and visual factors that contribute to it. First, we create samples by applying a flat white latex paint to standard gypsum wallboard. Two application methods: spraying and rolling are used. We then measure the BRDFs and textures of the samples and find differences at both the microscale and mesoscale that help explain the effects. Next we use the BRDF and texture data as input for a physically-based image synthesis algorithm, to generate realistic images of the surfaces under different viewing conditions. Finally we discuss ongoing work to use these computer graphics methods to generate stimuli for perceptual studies, and to develop a psychophysical model of the touch-up problem that relates physical differences in paint formulation and application methods to visual differences in surface appearance. The purpose of the model is to provide guidance for the development of methods to minimize the touch-up problem.