The thing with the coloring of Grievous in the movies is that his mask and plating are the color of bone not really yellow, because before Grievous was injured and put in that life suit he wore a warrior's mask made out of bone. The people who made his life suit replecated a new mask of similar style to his original to cover hisinjured head and colored his plating to match the color and style of it. So, for it to look right, his plating needs to be an off-white not a yellow. But I still think the white would look the best.