In this paper, we investigate the assessment of image realism by focusing our attention on the color compatibility between an inserted object and the background in an image composite. We propose a technique based on two color compatibility properties to achieve realistic image composition. The first property is related to the color similarity, and the second one to the consistence of color tendency between image regions. We further propose algorithms based on these two properties for image realism assessment and recoloring. These algorithms only require information from the image to be tested, making them suitable for practical applications where real images are unavailable. Effectiveness of the algorithms is demonstrated through various images and verified by ground truth.