Shida Beigpour, Christian Riess, Joost van de Weijer and Elli Angelopoulou recently published a paper, “Multi-Illuminant Estimation with Conditional Random Fields” in IEEE Transactions on Image Processing (TIP), 23(1), 2014, pages 83-95, in which they introduced a novel two-illuminant color constancy benchmark data set with ground truth. The images are available here and the original high resolution raw data from the camera (.X3F format) are available upon request. More information about the data set can be found at the project website.