When I create a .pdf from the Word file with the imported image, I can open the the .pdf in Illustrator to see what has happened to the color. The color in the image that was originally encoded 51:102:153 by Illustrator is changed to 31:97:205 in the .pdf output. The color in the table shading that was encoded by Word as 51:102:153 stays the same, i.e., it retains the Word color encoding.