A method of determining a color transformation for images of biological material includes preparing a first set of biological test objects using a first preparation method, and preparing a second set of biological test objects using a second preparation method. Each test object in the second set of test objects corresponding to a counterpart test object in the first set of test objects, the test object and its counterpart being of the same biological type of material. For each test object in the first and second set of test objects, the color of the test object is determined thereby generating a first and second set of colors The method further includes generating a conversion table indicating a mapping between the colors in the first set of colors and the corresponding colors in the second set of colors. The first and second preparation methods include first and second staining methods, respectively.