You can't change tool tip settings but you can change the color of labels. Just go to the object's Properties > Relation. At the bottom there should be two color buttons "Label color" and "Selected"-- that is, the color of the label when unselected or selected. You will get a prompt when you click on it asking if you want to use global colors. Choose no and you will be presented with the Color Chooser window. Choose your colors and you're done. You can't change the font size or type.