I noticed that I cannot change the colors of the label portion of a Multibox object. More interesingly, the background color of the label portion differs based on whether it is a Grid Style or not.
If a MultiBox has a Grid Style = On, the label area is gray. If the Grid Style = Off, the label area is white. The image is two MultiBoxes, with no space inbetween (which allows me to represent some values wider, but that's a different topic).