This paper reports an experimental method of measuring the colour change of wet paint when subject to a well-defined shear flow. Using a Multi-Pass Rheometer (MPR) and a modified colour spectrophotometer, the effect of shear on the colour changes of a red-pigmented paint were systematically studied. Substantial changes in paint colour during and after shear were observed for certain paint compositions. Additional direct optical observation on diluted paint samples strongly suggested that the key mechanism associated with the colour change was the state of pigment agglomerates during shear and the flocculation after shear. A model based on Mie scattering was developed to give a semi-quantitative prediction of the observed experimental trends. (C) 2003 Elsevier Science Ltd. All rights reserved.